Can I use Edge 510 as an indoor trainer computer I'm setting up for the winter (yes it's only October, this is Sweden). 

I need to set up a speedometer for my rear wheel while I use the turbo trainer, I have a Garmin Edge 510 with cadence sensor, and wonder can I set this up to feed cadence and speed (with speed taken from the rear wheel) to the Edge head unit whilst on a stationary trainer? 

How do I set the edge computer to deal with this (I assume it needs to know to take speed from the sensor and not GPS, and just trying to use it as normal failed).
I'm basing this on my 810 but I assume they're similar.

You can create a new profile for riding on the turbo. For each profile you can select which sensors are used. If you turn off GPS and turn on cadence and speed (and HR if you have it) you can use it indoors. You might need another sensor to pick up wheel speed if you only have a cadence sensor. A combined (speed and cadence) one is around £35 in the UK, not sure what they'd be in Sweden.

I don't have it on me at the moment. If you need more details I'll post instructions based on mine this evening.