Reply to Shift Key

Is it possible to create a (hold) shift key to temporarily change a modifier from 1 to 3? Due to the limit of 2 modifiers per input, i'm trying to incorporate a shift key into my effect bank selecting modifier. So, i've got one key that switches M1 between 1 and 2, and i wish to have another shift key that will hold 1>3 and 2>4? Thanks in advance!