Yeah.... don't do this. It's slower, a lot more clumsy, and as
@p.giannakis has already pointed out, it's a damn good way to accidentally bugger something up.
Cutting film leaders takes all of five seconds, and "Leica leaders" will work in every other camera, so there's no reason not to do it to any film you have lying around. I bulk load 80-99% of all film I shoot anyway (the number has dropped a bit of late as I've been playing with some other film stocks), but I spend five minutes cutting new leaders when a new order of commercially-rolled film comes in - usually while waiting for the kettle to boil or something.