I've thought of this too, depends on if you can get the numbers to work and/or if the dealers are desperate enough. There's sort of a void for them in the market right now that you can play to your advantage. Who's going to walk into a VW dealer and ask for a car that is outperformed by a new GTI, 5 years older, almost 1/2 the mpg, and costs more? As a trade in you are giving them a car that will sit for 2 weeks vs a car that will be on the lot for 8 months.
My conclusion was that IF the dealer will work with you on it, it can work out. Don't rush into it though.