I don't know for sure about pardons in particular, but the time-honored legal rule is to invoke the ex officio rule. Unwinding all his acts would be too disruptive to even seriously contemplate. This has happened, although typically at lower levels, like mayors.
Ultra vires too.
“Unwinding all his acts would be too disruptive to even seriously contemplate.”
No more disruptive than his actions have been. Since it was Pelosi that certified him qualified, let her bear the costs, and let’s prosecute the fraud and all those that enabled it. Tall lampposts and short ropes. 4th of July weekend festivities.