Many breweries in Portland will fill a corny for folks.
Is that an option for you?
If your transferring from a sanke to a corny I would try to set it up so that you can use CO2 to push the beer from keg to keg. IF, you haven't already been hand pumping AIR/O2 into the sanke, in which case I would just pour from the tap into the corny, carb it up and drink it FAST before it oxidizes if it hasn't already.