V.B.
What form are the supplements in? I mean... are they liquid, so you have to put them in something (or taste disgusting)? Or are they pills?
I wonder if you've ever tried just giving it to your child(ren) directly. That's how I have always given things to my kids. No hiding stuff in food.
"Here. You need to take this (medicine, vitamin, whatever). Do you want some juice/milk/water to wash it down with?"
Always worked for me! It might take them a few minutes to muster up the courage to down it, but they always managed somehow, with a little patience from me.
--
Oh, and my son used to take Nordic Naturals fish oil as well. Tiny little round gels and he'd swallow them right down, no problem.
---
If he is fully aware, then I'd let him try just swallowing them, and offering something yummy after. Let him have the "yummy" thing in hand before he takes the supplement, so that he can eat/drink it as soon after as is possible to help wash away the taste. It doesn't have to be a battle. Some kids actually prefer to get stuff like this over with quickly so they can move on. I know "I" would rather swallow a nasty pill and eat a bite of brownie or drink something good immediately after and get it over with, rather than know I had to sit and consume a full 12 oz glass of something the pill contents are diluted in. Part of it is mental, and part of it is the time/hassle of drinking the full glass of whatever, or eating the full bowl of whatever, etc.
Have you asked him if he'd like to try taking it whole? I would ask and give him suggestions about how to make it be over quickly. Starting with a glass of juice or whatever on hand.
If you do, be sure to read (if you don't already know) the best method for swallowing pills. It is NOT to put it in your mouth, add liquid (swallow of a drink) and till your head BACK. That causes the pill to float away from your throat and is counterproductive. ;)