I don't think there's any chance in hell that Dorsey would trade for a backup QB. Matt Flynn is not a starting QB. If you think he is, or may be, then you're a moron and you can stop reading here. For those who are not idiots, at least in acknowledging Matt Flynn is not a starting QB, during Dorsey's tenure with GB the Packers had a pattern. They would acquire young, low-cost (i.e. late draft picks or FA acquisitions) backup QBs, develop them, and then let them go - either through trade, FA, or expansion draft.
See: Mark Brunell, Ty Detmer, Doug Pederson, Matt Hasselbeck, Matt Flynn
This leads me to believe that Dorsey will acquire his backup QB(s) later in the draft or through free agency - not through a trade.