My former prof switched university and now I can't ask him in person for a LOR - should I try to see him?
I don't think a visit is necessary (and I don't see where in the linked thread it says otherwise). Even if you were to visit him, you would contact him first to make an appointment, presumably by email.

Why not send a mail in which you both ask for a letter of recommendation and whether the prof would like to talk to you to refresh his memory (be it in person or on the phone)?