Chances are you're going to need the triple shifter, although you might be able to make it work with the right double. You just need to make sure the length of the cage is sufficient, and double derailers might be a bit short for effective shifting. Friction shifting can cover a lot though.

I did just what you're describing, although I swapped the middle and outer ring, leaving me with a 46-22. The shifting on my setup is less than precise, but I don't have to do it very often.