#1 seems grammatically correct but not very elegant. Structure #2 is in principle neater but the word "to" doesn't sound right to me. Unfortunately, removing "to" still doesn't make the sentence very natural to my ear. I think the problem is the verb "make". "I made him play the piano" is fine, but when you try to invert the sentence it doesn't seem to work so well. If you must say it this way then I think I would try to choose another verb, such as "force", and use structure #2:

 

"He's the guy who I forced to play the piano."

 

Technically you should say "whom", but the juxtaposition of the casual "guy" and formal "whom" feels odd.