this is just me...but- you're not asking him to do it perfectly. you're asking him to DO IT. to me, that's not doing something i asked him to do - which means a time out. i have a 5 year old boy too....i know how stubborn they can be! which is why i feel it's important to really teach him that no matter how unpleasant something is, if it's something we have to do, tanrums/whining/crying/stalling are just not an option. you do it. or you get in time out. period.
**now, having read some other responses let me say- my son is not a huge fighter when it comes to this kind of stuff. maybe because i am strict about it, maybe because he just enjoys it more than some kids. but we have fun with this stuff too, we color and draw and do cutting and gluing on weekends for fun. so to him, it's not like trigonometry. i think that making it fun sounds great. he is so little still. but ya know, when it comes down to it, this is a good life lesson about having to do something that we don't really want to do. good luck!