I did them with function calls, I just pass the data from the button to a common function.
but this is basically what you need to set
joginc = mc.mcJogGetInc(inst,0); -- get the present increment
mc.mcMpgSetAxis(inst, encoderid, axisid); --mpg encoder , axis ; encoder 0, X axis 0
mc.mcMpgSetAccel(inst, encoderid, 15); -- 15%
mc.mcMpgSetRate(inst, encoderid, 100); --100
mc.mcMpgSetCountsPerDetent(inst, encoderid, 1); --one click give one incremental step
mc.mcMpgSetInc(inst, encoderid, joginc); -- pass the increments from the MPG encoder steps