Front mech question

As said above, it will require you to adjust the limit screws on the front mech to allow you change correctly.

I've not setup a double on a triple changer, but would have thought that you would adjust the inner limit screw to allow the changer to drop down to access the inner chain ring, then position 2 would shift you to the outer chain ring, and using the outer limit screw adjusted just a little further out, you could use the position 3 as the trimmming position for the outer ring to stop it rubbing the mech on the small cassette rings.

i've used bikes with a triple shifter and mech with a double chainset, with no ill effects. what are the problems you're having exactly?

my workflow would probably be:

1) fit the chainset and the mech but not the gear cable
2) adjust the inner limit screw until the chain runs freely through the mech on the inner ring
3) fit the cable with the lever set to 1, pull hand tight and secure
4) push the lever from 1 to 2 and back and check the shifting. sometimes you need to slightly adjust the angle of the mech to get the best upshift/downshift, or take up slack in the cable
5) try pushing the lever from 2 to 3: the chain may fall off the the outside of the big ring if so, adjust the outer limit screw

or something like that