Did plenty of research on supplementation for sick and FIP-afflicted cats. The general recommendations are (see references):

Vitamin A (liver, kidney, tuna, fish oil, eggs, butter, milk, NOT beta carotene in veggies)
Vitamin C (sodium ascorbate, ascorbic acid, tomato sauce/juice)
Vitamin E (egg yolks, butter are phytate-free sources, avoid greens and seed/nut oils)
Taurine (organ meat, trace amounts in Blue Wilderness large breed adult dry dog food)
Arginine (present in liver and muscle meat, preferably from free range/pasture raised animals)
Omega Fatty Acids: Omega-3 EPA/DHA/GLA (wild caught fish sources)

http://www.angelfire.com/fl/furryboots/fip.html
http://www.dr-addie.com/treatment.htm
http://www.peteducation.com/article.cfm?c=1+1400&aid=665
http://hpathy.com/veterinary-homeopathy/feline-infectious-peritonitis-fip-case-management-and-suggested-new-rubrics-developed-from-500-cases/
http://www.neighborhoodcats.org/how_to_nutrition
http://www.marksdailyapple.com/natural-cat-diet/

Drogo received 5mL liquid formula AM, 10mL total in PM.
Drank water from large bowl due to contaminated dish.
Within 1 hour, used 2 litterboxes.
1mL prednisolone in AM/PM.

CONCERN: New symptom of nasal discharge, wet breathing discovered in PM. At first I was alarmed that he might be displaying labored breathing due to chest effusion, but nose bubbles confirmed that he might have contracted a cold or respiratory infection.

Energy: Alert for new activity, but low energy both AM and PM
Movement: Mobile, requires effort, but will jump down from cage, walk over to bed or cat tree. Made a pass at scratching post.
Tracking: Slow tracking, not really interested. Have not introduced play.
Appetite: Did not observe him eating any hard food, force fed liquid formula
Attitude: Lethargic, appeared tired or subdued
Hygiene:Fur appears unkempt, he did groom himself in an attempt to clean matted hair on his throat, did #1 and #2
Hydration: Sipped from big bowl, took liquid formula

Internet literature suggests that cats prefer warm food to cold, so have to determine a better storage method.

Also feeding too much of the liquid formula induced vomiting in Conan, may have to rethink this formula to include extra Vitamin c.

This was a disheartening day overall as I am not very optimistic with Drogo’s lack of energy and progress.

Found some interesting (hopeful) reading regarding a homeopathic approach to treating FIP.

Went to work today so didn’t have much interaction with kitty. Drogo showed more energy in the morning, even ate twice and used litter box. He showed some interest in ball/string but did not give chase. He has been able to navigate up and down the cage with some effort.

As usual, showed considerable lethargy during evening. Was able to receive full morning and evening 1.5mL dosages of prednisolone. Watched ball/string but did not engage.

Energy: Alert in AM, low in PM
Movement: Mobile, but still has foot drag, requires effort
Tracking: Showed some interest in play, was slow to track string
Appetite: Dog food in AM/PM
Attitude: Lethargic, appeared tired or subdued
Hygiene:Fur appears unkempt, gave him a brushing but seemed a little sensitive, did #1 and #2
Hydration: Sipped a few times today

Drooled a lot when receiving dosages.

Morning IM:
he is back in the game room. he was messing with the ball/string for a minute and now he is kneading the bed
well he brought be the ball/string while i was playing
now he is batting at the string, i have it hanging on your chair
he is vocalizing for attention
he is definitely sharper, he is biting at it and swatting

Energy: Alert in AM, low in PM
Movement: Mobile
Tracking: Showed some interest in play, was slow to track string but was batting at it
Appetite: Dog food in AM/PM
Attitude: Lethargic, appeared tired or feverish?
Hygiene:Fur appears unkempt, gave him a brushing but seemed a little sensitive, did #1 and #2
Hydration: Sipped a few times today

He approached litter boxes in kitchen, but contemplated how to enter
He was more brisk with covering litter this evening
He did go to food bowl in cage around feeding time
He is more vocal today
He is watching ball/string today though didn’t seem to have energy to fetch

Stronger this morning, received full 1.5mL dosage. Indicators of #1 and #2 in litter, will investigate in evening. LS says he appears more bloated but eyes seem more focused

Energy: Low in AM, very low in PM
Movement: Plopped to floor in AM, very little activity in PM
Tracking: No interest in play, wasnt focused on play
Appetite: Dog food in AM, no food in evening
Attitude: Lethargic, appeared tired or feverish?
Hygiene:Fur appears unkempt, no bathroom visits observed
Hydration: Water bowl was 3/4 empty

Bad evening for Drogo, hardly any activity or appetite. Did not want to engage in play, was hunched most of the time.