Wireless bridge for embedded ethernet switch
Yes, you only need two wireless router/access points that can work as bridges. The cheapest ones have typically only one wireless interface and one wired interface, and they can be configured to just forward between the two interfaces (i.e. bridge them). 

After configuring both (this is often called "wireless adapter mode" in the manufacturer's software &amp; manuals), you connect one access point to the switch on the robot, the other to your laptop/home switch, and you're done.

The trick is to find access points that can work off low power, e.g. USB. (You don't want to replace the Ethernet cable with a power one after all ;) I myself have had success with the Asus WL-330 from Amazon. A colleague bought a TP-LINK Portable Wireless N Router last week and he says it has the same "bridge" functionality as the Asus, in addition to costing only 17EUR and using so little power that his Kill-a-watt can't measure it.

Hope that helps. Good luck!