Galvanic Isolation with Voltage Equalization?
I need to equalize the ground voltage between the input and output of
  an isolated dc-dc power supply while still maintaining galvanic
  isolation


If I had a black box with two wires going into it and was told that the two wires ARE NOT galvanically connected but, V1 always equals V2, then the only reasonable conclusion I could draw is that they ARE galvanically connected and they are indeed shorted.

Imagine putting your multimeter across the two wires - it would read zero ohms. It couldn't possibly read anything else because V1 = V2.