been thinking about this for a while and finally tried it. i bought a set of road bike sugino maxy cranks of ebay for £15, the kind with the built in chainwheel and i made sure the bcd was 110. it was a 52 tooth ring and it also had a 40 tooth ring bolted to it with sugino bolts. here's what i did.
the cranks before.

bolted on a sugino spider to mark it

the lines to cut to

a dremel and 20 minutes later

the piece you cut off makes a nice ninja throwing star

going to polish then paint them candy red, should look nice and cheap too.