Oh, yeah! It’s totally done and I forgot to come back here.
First, I made namespaces (/authority/imdb/film, name, character). Then I made properties that enumerate those namespaces and attached URI templates to them.
Check out the IMDb profile property on film. It expects Enumeration as its type. Then you have to get a little fancy and switch to the admin view. Set the Enumeration property of the property to the expected namespace. Then co-type the property as a Foreign key property and set a URI template. Set its type to URI Template and fill in both the canonical template (used to generate and recognize URIs) and the other templates (used only for recognition).
The schema UI will support this at some point… just not yet, as it’s kind of a power-user thing.