I have a spell, a ritual, called a tesla flexion. It should allow to talk to someone in an alternate timeline. We might be able to use it to talk to someone that created Derleth, or at least knows more about how it works.
It only lasts two minutes. I think if he believes he's speaking to his daughter, he'll be more likely to cooperate and try to help us as much as we can in the limited time we have.
We'll come up with what to say to him in advance and the questions we want to ask him. We just need someone to pose as his daughter. Within the tesla flexion, you can't touch each other anyway.