I dont see why the sti's wouldn't work, but if you want geared bullhorns, try bar-end shifters in the ends, with interuptor (cyclocross) levers clamped around the end.
You'll rund into a problem of running the shifter housing under the clamp of the brake levers, but Pyramid (J&B house brand) makes cyclocross levers in the larger diameter, and provides a shim. I filed down the shim to allow the shifter housing to pass through.
The barcons went from side to side, instead of up and down. I used (and love) suntour bar-ends. Some on ebay now: http://cgi.ebay.com/Suntour-Barcon-S...QQcmdZViewItem
With the above setup, you have braking and ****ing all in the same place, and rapid up and downshifts involve one motion (moving the lever) instead of several (clicking the STI several times).