Yes, you can set these samples to respond to any MIDI CC including your keyboard's modwheel, sliders, or you can use the graphic modwheel in UVI Workstation.
Simply set the CC value for that feature in the piano's interface to the corresponding MIDI controller you're using
For example, you could set the Una Corda pedal CC to a value of 1 for modwheel, then use your keyboard or UVI graphic modwheel to trigger the soft pedal.
This is also a great way to use Mute Strikes in the Ravenscroft 275 library if you don't have extra pedals.