there's a super tutorial on missouri star quilts. She uses a special ruler (which I've bought a couple of weeks ago, but haven't yet used). But I think with a little thought, you could make a template using heavy template plastic.
http://www.youtube.com/missouriquilt.../8/rIHhTxTpMQ0
there's also a tutorial on this board, but the instructional photos are missing (finished photos on page 3 of posting)
http://www.quiltingboard.com/t-25080-3.htm