I could be completely wrong here, but I don't think ProSeries has EVER accommodated the payment dates for extended deadlines due to state disasters.  Assuming that is the case, I doubt if they ever will.

The taxpayers need to suck it up.  If they want the convenience of you setting up the payment, they can pay it on April 15th.  If they really want to pay it later, they need to take responsibility and pay it.  Your clients are not children; they should know how to pay their own bills by themselves.