Joined: Jan 2010
Posts: 9,833
Likes: 1,809
From: Northern California
Bikes: Cheltenham-Pedersen racer, Boulder F/S Paris-Roubaix, Varsity racer, '52 Christophe, '62 Continental, '92 Merckx, '75 Limongi, '76 Presto, '72 Gitane SC, '71 Schwinn SS, etc.
I have successfully used triple-specific left STI levers to operate normal double arrangements. The trick was to set it up using the shifter's 1st and 2nd detents, with the 3rd detent locked out against the hi-limit screw.
Also, there won't be fully-functioning trim positions at the big-ring position, but which can be adjusted around with fine-tuning (and/or by very slightly widening the cage width near the front of the cage). Done this many times actually.