http://www.axess-electronics.com and check out the amp switcher/audio looper and midi pedal. email mario and tell him what you want to do. he will get back to you pronto.
or
http://www.voodoolab.com and check out the gcx audio switcher / ground controller (what I use for now). as your DR switches with TRS 1/4" phono plugs, you can handle these through the send jacks on the audio switcher. make program changes to switch the VH4. I mostly use it to activate the channel inserts and select the pedals in the inserts. easy to program too. run you about 800 bucks for the set up.
or
http://www.customaudioelectronics.com and check out the 4x4 audio switcher and RS10 midi controller and really spend some bucks on top of the line gear.
or
use a cheap midi pedal to switch the Vh4 and use your mesa footswitch for the DR.
Steve