That's something that definitely hadn't been considered.
The small size looks like this:
http://www.aswexpress.com/discount-a...Fa1xQgodI2IAOA
and these, sliced in half, as the large.
http://www.aswexpress.com/discount-a...anvas-pad.html
Prices could probably be bumped up slightly. A 3x3 inch frame may be difficult to find.
This is good, thank you Xidelt for your input.