using double driver for y axis (2 replies)

i have ready ramps 1.4 with drivers, motors etc and i wanna use what i already have.
i wanna use only 2 axis (with laser engraver attachment) but 3 drivers. 1 for x and 2 for y. there is x, y, z, e0 and e1 slots on ramps so it should be ok.

i want to make one of those slots/drivers work synchronized with y driver. i am guessing it should be fairly easy but i couldn't figure out.

how can i synchronize them in firmware? version is 2.0.5.3