Far as I know, if the sample set in question has more than 3 expression pedals it shouldn't be an issue. If you've got the extra expression pedal to operate it, you should be able to 'auto-detect' it and use it to control additional virtual expression pedals. Another way to look at it, if you can operate it with your computer mouse, you should be able to operate it with a pedal that's connected via MIDI.
Marc