There's a video on YouTube that shows how to install a tension belt using a pair of vice grips on the crankshaft pulley. I followed the method and it worked very easily and without needing to purchase extra tools just for one job!
You basically install the belt on the smaller pulley first and get it started on the crankshaft pulley as much as possible. Tightly place your vice grips on the outer crankshaft pulley lip (front of vehicle) right where the belt begins to come off the crankshaft pulley. Use a breaker bar to slowly spin the crankshaft and the vice grips will force the belt onto the pulley as it turns. Check out the
StarknightMT guide on how to change a drive belt: a comprehensive guide for more detailed visuals on this technique. No special tools required and works like a charm! A little patience will get you there.