You probably wouldn't have to start entirely from scratch. If someone says wagh vIghro'mey tIQ. qarbe''a'?, even though this isn't a usual tag question, I can deduce that qarbe''a' is probably supposed to refer to the previous statement. (Perhaps they originally said wagh vIghro'mey tIQ confidently, but then realized they weren't 100% sure, so they added qarbe''a', in the sense of "...am I wrong?") It might not have the same connotations of expecting a "yes" answer, but you're still asking about the accuracy of a statement.