Not sure that trying to set constant velocity within the controller is the only or best way to do this. Modern toolpaths and post processors can achieve complete control over speeds and (more importantly) accelerations, as well as include smoothing functions either within the post processor or the controller itself, if that is best.

Not sure how you create your toolpaths but the likes of Fusion 360 are very much up to date and there is the added benefit of an active and responsive forum where you could ask about this in the CAM area.