I have Mariner's Compass Block Factory from Quilt Pro and they have 20 point blocks. One of them is exactly like the small center of this block and you can make it any size you want. You might want to start with that program and see if any of the other 20 point blocks can be revised to meet your needs. You can't alter the blocks in the program, but you could change them after you've printed out the paper pieces.
Hope this helps!
Lynda