I do a feint like a mawashi geri and follow with the Ura... Or I do it in two steps, first mawashi geri - I come back to my first position and then I do ura mawashi geri.
Ushiro Ura Mawashi Geri
I use it when I'm very close to the line, just before going out of bounds. I wait for my opponent to attack me then strike as he comes in.
