The MityVac won't work. The VCV operates by bleeding off vacuum at a controlled rate... the MityVac simply can't produce enough volume. Either the HF venturi pump, or a second vehicle, will be required to supply the vacuum. Or, you can do it with the engine running.

Another option is to connect a vac gauge to the output of the VCV with a long length of hose, so you can view the vacuum while driving the car. And also disconnect the kickdown solenoid at the back of the tranny, and the Bowden cable. That will allow you to move the throttle between idle and WOT while driving, without the transmission downshifting.