You can get out of grinds/slides without ollie if your grind/slide reached the end of a rail, etc. Just align your skater where he will not bail if landed. But if you want a smith to boardslide combo, etc. you'll need to ollie first.
Yep putting it on cancel trick button is the right move :) it is cancelling the trick itself - if you just want to do a short slide/grind. But if you are doing tail/nose, etc. you still have to align your skater to land :) and I'm ok with that.
