the 500D doesn't have a PC sync cord socket, plus the PC sync socket on the 580EXII is just for triggering the 580EXII itself, so it can receive signals but can't send..
Constantly mounting a 580II just to trigger the DL might get tiring if hand-held.
TS should get a cheap hotshot adapter or radio trigger.
I have a almost new spare hotshoe adapter if TS is interested.