But the short answer is, "probably not." Jackets (whether sports jackets or suit jackets) benefit from being stored on properly sized and contoured hangers. To fail to do so runs a real risk of unsightly "shoulder bumps," at the very least.
Since a perfectly fine, wooden, contoured jacket hanger can be had for about five bucks, it's foolish to cheap out on this expense. However, if you're dead set on hanging your blazer on a plastic hanger anyway, at least consider padding the hanger in the appropriate places with foam, or cardboard, or something. Although, again, a proper suit hanger is so inexpensive, so unlikely to ever wear out, and so likely to always come in handy, it seems silly to me to attempt to create a makeshift version out of a cheap plastic hanger, cardboard, and foam rubber.