Otter are tough to get off the stretcher anyway so I think you are going to have to rehydate and restretch. I don't think I would soak in a tub though. I would just wrap in some wet towels.
If your stretchers have a lot of taper you can try giveing the nose of the stretcher a sharp blow to the floor. That will sometimes get a stuck pelt started but not as likely with otter.