We have this EXACT problem. DS is rolling over before I've even put him down! Nothing will distract him and I've resorted to changing nappies standing up. We now use the nappy pants, I ran out and had to use flats the other day and it was HELL. I truly feel you pain.
I don't have any advice, just wanted you to know you are not alone.

With holding her down, I change him on the floor now and put my feet firmly but gently on his shoulders. He HATES it, screams bloody murder but he does that anyway.