How To Reinstall A Drive Belt On A Craftsman Push Mower?

I have a 21" self-propelled Sears Craftsman mower, model 917377563. The propelled drive wheels locked up, so I checked the relatively new front wheels (they're ok) and the sprockets they attach to (also ok). Since the drive belt is the original one for this 6+ year-old mower, I bought the drive belt kit from Sears that includes the belt and the spring/spring holder. My problem is that I can't get the new belt to stretch far enough to wrap around the front drive pulley while it's wrapped around the engine/blade drive shaft. I've tried pushing in the pulley and drive mechanism using a heavy bar, but it's just not quite enough for the belt to wrap around the pulley - I probably lack about 1/4" of belt length in order to get on the pulley. There was also no slack on the old belt - I had to cut it in order to remove it. Is there a secret to reinstalling new drive belts? I considered removing the drive pulley, but then I doubt if I would have the leverage to rebolt it into the drive mechanism once the belt was wrapped around it.

Any help is greatly appreciated.