How long a stretch do you usually need to maintain that drop postition for? I'm asking because if you only need to get 'aero' for short periods you can try what I've done on my two bikes. One has riser bars and one has 26mm diameter mustache bars. what I've done on both is to simply slide a pair of inexpensive barends as far inboard, inside the shifters and brake levers, as I can. This allows me to get into a pretty effective aero tuck when I'm riding into a nasty headwind or just want to get going as fast as I can. there's no arm rests, so it's not a position you'd want to hold for an hour. But it's a cheap and quick way of adding another hand position to shift to. And that helps keep you comfortable over the long haul on a mountain or comfort type bike.
DanO