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.