beveling foamcore

I am trying to bevel cut 20x30 foamcore into 1/2 inch strips. I have tried using a hand held mat cutter (not deep enough and not adjustable) and also using a foamboard cutter (FABULOUS but not mounted to straightedge -read- ***NOT*** dummyproof.
My foamboard cutter blade won't fit into mat cutter "slot".

Aside from building my own base and straightedge "attachment", does anyone have any suggestions?

Thank you in advance.
~melissa

I don't know the secret but, I may have a clue to offer. Some friends studying Architecture in college built foam core models of the buildings they were designing and used to cut it this way.

Thank you, GausianNoise...I will check into that, and as for my lookout- thank you, as well!

~melissa