The alpha version of WarpPipe, an online tunneling tunneling service, recently launched and has been confirmed to run at a full 55-60 frames per second. Games being supported include 1080: Avalanche, Kirby's Air Ride and... drum roll please... Mario Kart: Double Dash!
To get it to work you need a GC, broadband adapter, router and broadband connection.
I've got everything except the GC broadband adapter so far, but as soon as it gets here, wooo! I'm so frickin' excited to try this out.