The Back course may have been used for departures at some time, but is probably rare. One might confuse your question with the case of using the front course for guidance when departing the reciprocal runway. This was done at the old Hong Kong (Kai Tak) when the 31 ILS was used to depart 13, but it was NOT the back course being used.
Back course approaches were relatively common years ago, when a normal ILS installation gave a "free" approach signal for a procedure on the reciprocal runway. I believe modern ILS installations, in producing much better quality front course signals, may not now provide a useable back course, and the procedure is not much in evidence these days.
ILS may certainly be received well beyond the rated coverage of the aid, but should not be considered suitable for autoflight (which appears to be the subject of your question??)