I wrote my advise inthe wrong place.. I too have a great idea but it's in the advise column.. sorry!

I did it in the bath. Especially when my daughter was small, she was SO ENTHRALLED by the bath and bubbles, she was completely preoccupied. And cutting wet hair, I find to be easier. So, she'd sit in her bath seat and play with toys and bubbles and I'd snip a few and be done with it!