How can I programme a single key for a Ford Focus?

I had two keys for my Ford Focus but lost one of them. On trying the spare it doesn't work when I turn it in the ignition. The red light on the dash is flashing, indicating that the key needs to be programmed. But it looks like I need two keys in order to do this. Is there any way round this as I can't afford to take it to a dealer and pay them? Thanks :)