Back to the Bat in question
I take it you start at the larger diameter, then as you traverse, the diameter gets smaller, and you want to increase the feed rate - for what purpose - to get an even finish?? I take it these are aluminium bats, perhaps ( maybe showing my ignorance)
I think Overloaded has the answer. I take it the spindle speed of your machine is automatically variable.
If not you might consider a Macro written is Visual Basic
Something like While Is moving
Feedrate is proportional to X axis distance
Code F etc
Wend
(That is not the syntax - but you get the idea - While is moving is in the syntax - usually to STOP anything else happening. You can adjust the feedrate by getting the present readout from the DRO (either X or Y I suppose) apply a multplier, and have the macro pump out the new feedrate.
You might prefer to do a Macro like this, because you can control all the various parameters. The is a Macro Tutorial (Scripting) which gives you the idea of how to do one.