Christina:
As a mom and a nurse that has worked in pediatrics, here is what I have done:
Plan A: My daughter has to take medicine for asthma every day. She is 2 and we were given powder to mix with food. That was a huge struggle and we wasted a lot of medicine. We discovered that there was a chewable tab in the same dose and have switched to that....weirdly she loves it and "my medicine" is part of her daily routine.
Plan B: if you can't find some type of solution to get him to do it voluntarily (which at this age they usually don't) here is the next option...
Use the smallest syringe dropper that will fit all the medicine in (3 ml syringe works well with this age). Hold him in lap with arm closest to you tucked behind you. Hold the other arm and hold his face against your chest. Take syringe and slide it into check on outside of teeth (have to have it in far enough that they can't spit it out) and gently squirt in a little at a time till gone. You can also just hold him and have another person do the syringe. Get everything ready, then do it quickly and its over. Give lots of cuddles, loves, or stickers/priase when done.
this is less drawn out and I find less tramatic...child has less time to get worked up etc. I would not recommend putting it in bottle or drinks....I have found that kids then associate something "bad" with bottle/cup (with long term medicines) and it can make problems to get them to drink afterwards.
Good luck-this is a toughie!!