The only gizmo I can think of is a wireless ethernet bridge. they sort of look like routers and their ethernet port plugs into the device in question (xbox 360 here) to turn it into a wireless gadget. so your 360 would think it was hard wired to a router, but the bridge is actually connected to it via wifi.
fwiw i used to use one with my PC. I tried it on my 360 and 10 minutes later i was drilling holes and running cat6. it was just far too slow for my uses (windows media center extender).