Since you've gone full Frankenbike anyway, you could try River City's Reach Around Fender Brackets: River City Bicycles Reacharound Fender Brackets - River City Bicycles Portland, OR

Basically the idea is that you cut the fender in half and these brackets connect the two pieces while bridging over the brake calipers.

You just need to make sure you've got the toe clearance for fenders.