After a wrist injury, I put a BMX bar on my Stumpy, and it was nice, except sketchy on steep climbing and really increased wind resistance, you won't set any speed records. The first MTBs in Marin County (Klunkerz) used BMX bars in the 70s, so I just copycatted an old idea for a new reason.

Cost factors: bar, 22.4 mm stem, longer cables and housing possible.

Inconvenience factors: The acute riser bar bend requires creative positioning of Rapid-Fire (I had to put mine upside down), but twist-grip shifters should fit. (I bought some on sale, but the triggers worked fine once I got used to the odd positioning, even wearing thick double mittens. I also had to cut slots my Ergon grips as triggers hit them and blocked shifting. ) It's possible that integrated shifter-brake lever units might fit fine.

Pluses: "double-decker" cross bar and bottom central bar provide lots of room for stuff like computer, airzound horn, double headlights, battery packs, front bag...

If this sounds Fredish, it is, but it sure took the pressure of my wrist and made it possible to ride rather than sit the winter out. Sitting up is also easier on your neck.