Enter the town menu via a script.

Hmm, I think it can be implemented using workarounds. You need to hide the town in an inaccessible and unexplored area, and then create a script like this:

MakeHeroInteractWithObject(hero, "Town") -- Use this for interacting with the town

function ResetOwner(hero, obj, old, new)
  SetObjectOwner(obj, 0) -- Set the town's owner to neutral, as MakeHeroInteract will simulate capturing the town
end

Trigger(OBJECT_CAPTURE_TRIGGER, "Town", "ResetOwner")

I haven't tried this implementation, but it would be interesting to see if it works.