Generally, barcons fit road bars, not mountain bars. The only exception I can think of is the steel Albatross bar sold by Rivendell. The steel is so thin that they take mountain shifters and brake levers, and barcons will fit. It might possible to modify the barcons to fit the smaller diameter mountain bars. I don't know.

It's possible to tuck the end of the tape into the bars with barcons if the tape is thin and the tape enters the bars without bunching up or wrinkling. My Peugeot has two layers of cloth tape tucked in:
http://community.webshots.com/photo/...8014369GPeTnK#

Maybe you could use Paul Thumbies with trekking bars.