Hey nialman,
Annoying isn't it?! I always found a wire coat hanger opened out with the hook squashed a closer together and fish like a madman!!You will be able to widen the hole,not too much, in the wall a bit to make it easier for yourself because the fiting you put on will cover the hole.
On a serious note tho sounds to me that the wall lights are controled by the dimmer(should never be fed from sockets) and so the cable in the wall could be live so make sure the circuit is dead before fishing starts.If your unsure dont risk it.A good sparks will do it cheaply.