A ladies fixie with a tricky brief

If I am buying another brake set, I could really do with one of those upside-down rear brakes (because of the mixte frame, the brake cable arrives at the caliper from beneath not above as normal). Anyone have any idea if I can buy a modern replacement for one of these?

Do you need to get a new set if you mount the brake here:

This is the most distinctive feature of the frame - I haven't seen this kind of triangular bridge before.

/attachments/61495

Kinda like this
http://upload.wikimedia.org/wikipedia/commons/f/fc/Peugeot_Mixte,_PX18.JPG