Nope, haven't tried it.
So you mean on a temporary basis, with you retaining control?
Under 'Manage' beside each site on the main page, there's an option to 'Add or remove owners', where you invite them by email address.
But I think that's the same thing, just bypassing the verification stage, they'll still have authority to add or remove additional owners (presumably including removing you).
I don't know know of a way of sharing the data without them having admin authority