How to give infant supplements?

My 6 month old son needs two supplements - iron (fer-in-sol) and Vit D (di-vi-sol). He is fed on demand throughout the day and has one bottle (expressed milk) before bed. Up until recently I have just added the supplements to his nightly bottle - he has now discovered that he doesn't like the taste of his vitamins (or possibly doesn't like the bottle) anymore and will refuse to drink anything that has the supplements in. I have tried watered down apple juice and milk. He is just starting solids and is only eating cereal now - but next week he will start veggies. Any suggestions on how to get him to take the supplements??