If you are using a road FD, you’ll need a road compatible shifter. I think you can fudge with a mtb shifter because I think it pulls more cable. The cable will have to have some slack.
The easier approach is to use a thumb shifter. This is what I’m using on a flat bar 2x7. With a 2x, there really isn’t any advantage indexing as the lever moves one way to shift up and the other to shift down.
John