Maybe try giving him a small handful of feed packed with garlic. His taste buds/sense of smell should then be overwhelmed/confused enough not to then smell/taste the meds in his 'proper' feed.
Then just prepare and present his feed as normal as you would every other day so he has no reason to be suspicious about it, even add a bit of garlic to that too if he's a slow eater or has a larger feed.
Sometimes they become are suspicious because subconciously your HR/breathing are slightly elevated (or other subtle changes they pick up on) so acting blase like you aren't trying to
poison them can also be half the battle!
I did have one that would only eat meds if you smothered the feed in molasses and hand fed while telling him how amazing, wonderful and brave he was....