To be perfectly honest... I don't know!
There is, however, a dim and distant bell ringing that's telling me this has been approached before, so hopefully someone may be able to help. My guess is you would have to have at least one waypoint in your flightplan and then by rights it 'should' work as a normal flight.
One other thing you could do also is to create a flightplan to somewhere else, take off, declare and emergency and then when asked if you can make it back to your departure airport, select 'yes'.
Would be interested to know if you work out a successful solution