Hi, Mike.
You'll want to look in the VoiceAttack help document and search for, 'Joystick Button Recognition'. You'll be able to assign a button from your wheel as a joystick. Note that you'll have to assign your wheel as a joystick in VoiceAttack first. For more information on assigning your joysticks, see, 'Joystick Options' for the Options screen.
Hope that helps!