Here is the solution as given by Cam over at OSCUlator
Flip the main view to to the Scalings Page (choose View->Flip to Scalings Page or Command-F) and locate the message for your button. Then change Output Min and Output Max to the desired value. If a MIDI CC message is already assigned, you just have to enter for example the value 7 if this the MIDI value (between 0 and 127).
Works a treat !!! Full preset control at last !