I wrote a scriptlet to flexibly set a note range with a lower and upper splitpoint and a selectable number of notes for the velocity slope (up to 1 octave). The resulting velocity value for the played notes within the lower and upper slope areas will then be evenly adjusted over the corresponding key range.
That way the scriptlet could also be used to set up various splits for diffrent sounds, but with overlapping key ranges (velocity wise). Just put it between a MIDI-In block and a VST. You could also use multiple scriptlets being fed from one single MIDI-block…
The parameters of the scriptlet can then be mapped to widgets and/or midi controllers.
I think, this could be a helpful little tool for some occasions.
Note: There isn’t any checking for meaningful settings, so you theoretically could set the higher splitpoint lower then the lower splitpoint… i don’t know how “robust” GigPerformer is, regarding such unwanted eventualities… just be aware of that, and better don’t do it! 
vel-slope-split.gig (65.6 KB)
Maybe this helps…