What's your chainline actually like in the small-small region? Lots of doubles have the cranks offset a bit to the outside, making those ratios quite well-behaved.

I think you also might be overly worried about straight chainline if you're nervous about spending a lot of time in the middle ring of a triple with the chain offset a couple cogs off-center.
If anything, I consider a bit of such offset toward the small gears in back ideal; uphills require more shifting to lower gears than downhills require to upper gears, so it's best to be centered a little toward the higher ratios on the flats. Gives you more room to shift without changing to another ring.