There are other 2 speed crank options besides Schlumpf. The Sram Hammerschmidt, although it freewheels so there goes the fixed gear, also FSA is coming out with one called the Patterson. Not sure if that one has hit the market yet or when it will.
From what I've read about it, the FSA unit has the fewest requirements for mounting. No chamfering required as there is for the Schlumpf, and ISCG mounts not required as they are for the Hammerschmidt.