Putting a cap on the value of a MIDI-mapped parameter

I have a session where I'm using an expression pedal (cc11) to control a pitch shifting plugin. The pitch shifter can shift up or shift down, but I only want to shift down, so I mapped the pedal to the bottom half of the shifter's range, as you can see in this screenshot. So when I push the pedal heel all the way down, the shifter is shifting down a full octave, and when the toe is all the way down, the plugin goes up to zero, and doesn't apply any pitch shifting at all. This mostly seems to work fine, but the problem is that sometimes when I come up to zero too fast, it will momentarily shift up a half step.

So my question is -- is there a way to put a cap on the mapped parameter's value? I don't know if this is something that requires M4L to solve, but it certainly doesn't seem to be fixable within the MIDI Mappings panel. I can just change the max value to .49 because then it will usually not come all the way up to zero.

If anyone has any ideas, using M4L or just using Live's built-in tools, I'd be most grateful. Thanks!