My 6,5 month daughter despises her tummy time. She has to be kept occupied all the time with toys while on her belly, otherwise she starts fussing and, very soon after that, crying. While playing with us, she has little need to crawl, since she's ok and busy where she is. When she's fussing or crying, she won't be trying to crawl, she just tries to roll to her back (not too good at it yet).
We tried to put toys in front of her so that she would try to reach them, but it hardly affects her non-fussy time span. We tried putting her on various surfaces (her mat is not the best for crawling) like a carpet or panel-floor. Didn't make much difference either.