My little man hated tummy time too (he'd just SCREAM the whole time)...I found that the only way I could get him to strenghten his neck was to put him up over my shoulder at every chance (while burping, walking, sitting etc)...then as his reflux got a bit moreunder control we propped him up on a pillow for short bursts...these days he's still not keen on being on his tummy but it is getting better/easier...

Good luck!