There are more options for brakes:

http://problemsolversbike.com/products/cable_doubler/

http://www.sourcebmx.com/product/components/bmx-brake-levers/odyssey-m2-lever/7741.shtml

And even a blingy double lever from Paul Components 😀

I have seen the two stem system work well, albeit with less of a discrepency.

I’d suggest that finding a workable position with 2 bars and 2 stems is the best starting point, then get someone to recreate that position by making a single bar from scratch. I’d be willing to knock something up once the position is finalised, would be steel and welded sections not bends. Might be best to try to find someone local (if we aren’t)

I’m happy to discuss via email – matt@18bikes.co.uk even if you don’t want me to make it

Matt