I just found this on the net re Stamp Lift.
Quote:
so you can brush this on your stamp or best on the part of the envelope on the back of the stamp, This will eventually loosen the gum so you can remove your stamp. IT WILL NOT REMOVE THE GUM JUST LOOSEN IT, then carefully with a cloth slightly damped with water clean the gum off the back of the stamp, Do not leave the gum on the stamp. This can cause cracking or discolour your stamp in time after this treatment.
If he is right then I might as well soak them instead going through all this.