Add local offset stops when cursor reaches screen edge

Suprised I couldn’t find anything on this, it seems like it would be a common problem.

I’m using Mouse X and Mouse Y as axis mappings, with a check for MMB Pressed, to add local offset to a spring arm. This is my setup:

The spring arm moves fine until the cursor reaches the screen edge, after which moving the mouse in that direction does nothing (acts a lot like a clamp).

Only after I release and repress the MMB will the offseting begin again. Any ideas how I can get continuous movement regardless of cursor location?

Thanks for your help