using 2500 with V Drums

I'm having problems trying to simulate the open hi hat/close hit hat sound using my v drums with my mpc 2500- I know how to do it on the mpc's internal pads but does anyone know how to work it so that when I take my foot off the pedal on my v drums I can simulate the open hi hat noise because currently I can only make the open hi hat noise when I step on the pedal!