I just bought a binding tool to help with that kind of stuff.
It was only $6 at my local quilt shop and it does several angles.
http://www.animasquilts.com/AQPtools1.html
There are a few tutorials online hon how to use it as well. I'm looking forward to using it next week. I'm going to make a bunch of not square things and try it out :)
Maybe something like that will help out.