AS you say, use a C clamp to re-compress it and then install a 10mm bolt to keep it in that position. Clamp it slowly or it will break.After the belt and idlers/tensioner are in stalled, and of course it's all lined up right (white belt lines line up with cam/crank dimples-that's all that matters), set it as shown in this guide and remove the bolt. It's easy but sometimes it takes a few tries to get it right.
http://zhome.com/ZCMnL/PICS/ti....html
Read near the end where it starts as:
"Here is the rest of the timing belt replacement procedure. "