If you are a rogue or bard and have the improved disguise (?) AA, you can effectively get two charges on the stone.
Assuming you're out of charges, you go into Neriak (sneaking if necessary), get a charge, go to a safe place, put on the froglok illusion. Sneak back and get the stone recharged again, then leave Neriak.
Now you have the froglok illusion till the next time you die, and you have one charge left for after you die.
Edited, Thu Aug 18 19:50:04 2005