[SixOfSpades]

There's also a way to do it without Stone to Flesh: Just leave Yoshimo in the Copper Coronet, or bott him from the party and send him back. When you re-enter the building, he will immediately die, as a result of his geas taking effect. BUT--a character wearing Boots of Speed can run up to him and talk to him before he dies, and recruit him back into the party. He will accept, the dialogue will end, and he will instantly die. But, because he's in the party, you can easily Raise him again, and no harm done.

I should note that this might conflict with the designers' intentions, but there is a loophole in the wording of the geas: Yoshimo described its effects as "it hurts, and then you die," not "it hurts, and then you die with no chance of resurrection."