-) U can use the dedicated electronic handle-flashlight. By modifying the cable for greater length you would get more freedom.
-) Via an adapter (linear socket/PC) you can use a non-dedicated flashlight of any kind. If this has the same guide number as the bar-flash there will be no problem. Otherwise set the flash output accordingly or look up the apertures the camera will chose according to the focal distance and chose the flash AE-setting respectively.