No, you can't use "normal" paper. Give it a try and you'll se, toner just sticks too well to normal paper and will take crisps of toner of copper. And that's not my theory, but there are a lot of people arround me, that use same technique. It simply works 
@edit: No, really... reeeeeeally, it doesn't perform well with white paper, no matter the printer settings, no matther the printer model. You should print circuits at highest quality anyway.
It's quite impossible to modify the laser printer, I know a few people tryed that but failed. PCB needs more passings through heater than just one. It's too haevy to be warmed up enough in that second...
Regards