Put the cryovac in the kitchen sink, and fill it with cool water, changing it out every 30 minutes. You might get lucky enough to get most of it defrosted, so that you could start it tonight. If the center core is still frozen it would thaw during cooking, and pose no real hazard since the part of the meat that will still be between 40 and 140° for several hours is not on the outer surface.
I usually don't freeze the cryovac butts I get from Sam's as they always have a date on them that's about 10 days out. That typically gives me two weekends to decide to cook them. Important to note here: I have only a small freezer, and Sam's is about 1 mile away.