Instead of soldering a 10K resistor, you can hold a piece of wire against the two pads that you're meant to solder the resistor on. While holding that wire in place, briefly connect and then disconnect the two pads of the 6-pin header next to the 8U2 shown in the tutorial http://arduino.cc/en/Hacking/DFUProgramming8U2 (reset and ground). Then, release the wire that you're holding against the two pads on the back of the board. This should put the board in DFU mode. It requires a bit of dexterity, but no soldering.