This doesn't make sense. If it's not voluntary then it's not a choice. I don't choose to sneeze, or to bleed when shot.Making a Willpower check (or whatever) is not a voluntary choice. You can no more resist doing this thing, than you can resist bleeding out when you've been shot. You don't want to do it, but you do it anyway, because you have no choice.
Role-playing is only concerned with the process of making choices.
But the typical compulsion to steal that might be resolved in GURPS by rolling dice is not involuntary kleptomania. It is succumbing to temptation, which is a choice and hence, as @chaochou said, is not well-modelled as a saving throw.