According to CGEL:
"The tag normally mirrors the subject and auxiliary of the main clause...There are exceptions, however, with verbs like suppose when they are introduced by a 1st person subject and followed by a that-clause: I suppose you're not serious, are you?; I don't suppose you're serious, are you?"
I haven't been able to find sentences like the one being discussed here.
Although, strictly speaking, this is not the subject of this thread, I just wanted to share what CGEL has to say on this "sarcastic" use of tags(which seems similar to the "antagonistic" use of tags we discussed a while back):
"There is a type of tag question in which both statement and question are positive...Its effect may be scolding(Oh, you've had another accident, have you?), sarcastic (So that's your game, is it?) or sarcastically contradictory(So your car is outside, is it?)"