My new "Road Bike" can best be described as a hybrid. Cyclocross frame, fork, wheels & tires, with a mountain bike drivetrain. I'm a fan of bullhorn handle-bars, most comfortable/familiar with SRAM mountain trigger shifters, wanted to give reverse levers a try, and didn't want to spend the money on road combo brake/shift levers.
I knew the new(er) SRAM shifters have detachable clamp, which gave me the idea to find a way to use them. I picked up a pair used, on ebay for $35, which is about 50% of the street price. The total price for brake/shift levers is about $65, compared to $200 for an entry level road combo lever.
I tried finding a larger clamp, for this purpose, but had no luck. I had some 1/2" thick aluminum in the garage, and ultimately the clamp I need is a refinement of a piece of aluminum with a 23.8-26.0 mm hole in it.
That's how the machining (on a drill press) started - I drilled a couple of 1" holes in my 1/2" aluminum plate. I added the through-hole and counter-bore for the clamp/fastener bolt. Then I trimmed away some excess material.
It's not finished. I still need to make a groove where it mounts to the shifter mechanism (keeping the shifter from twisting), trim away more material, and generally clean it up. But a quick mock-up illustrates that it's on it's way to doing the intended job.
Update: June, 2013
I've had these on the bike for over a year now.
As you can see I cleaned them up, rounded them off, etc.
There's not a lot to say - life with them has been uneventful. They work well, feel comfortable and "right" on the bike. As you can see they're pushed in pretty close. A mountain bike bar is a lot wider than the 40cm bullhorn I have on these. The up-shift levers hit my bar tape a little, and sometimes the lever sticks in the forward position.
From the front you can see that the shifters overlap each other. The shifter for the front 3 rings is cocked at an angle to clear his neighbor (the shifter for the rear 9). That was something I sorted out when mocking it up. In the time I've ridden them, I haven't really longed for a different shifting system.
Recently, I signed up for a century, and in training I realize that my hand discomfort on the bike starts to bother me after about 3 hours of riding. That motivated me to try out aerobars (with a wider, 46cm, bullhorn bar) - for one more riding position, and secondarily to make those 100 miles go by a little faster (presuming I'm going alone a few times throughout the day).
As it turns out, those areobars will fit the mountain shifters, with their original brackets. I've only done a few rides with these, but I can't say there are any real draw-backs, related to them being mountain shifters, and given my goals & expectations.