As
@slowmotion's said, there should be sufficient copper to solder one wire to the bit marker "W". If you follow the track on the other side, it goes to a large bare copper pad on the top right hand of the circuit board. You should be able to use that to solder your other wire to. Just clean the copper (a little meths on a cotton bud will be fine) and tin both the pcb pads and the bare copper ends of the wires with solder before soldering them together. Also, use a decent flux cored lead solder; the lead free stuff's hopeless.
