I thought I had replied to this yesterday - I don't think so - but why do you need it.
Mach3 will respond to CSS - Constant surface speed - where you are taking a cut across the face of work on a lathe - and the SPINDLE will accelerate to keep the speed pf the work past the tool constant. I suppose, but have not tried it, that this would also be the same cutting a taper shape. For this, though, the spindle speed must be controlled by Mach3.
The problem is the GCode can only have one instruction (of each type) on a line - so one F instruction is all you can have. You could split the line into say 5 lines, and increse the Feed in each one, if you have Constant Velocity on the effect would not be too bad. - BUT why do you need it.