This is what masking tape and a permanent marker pen were invented for! But I think if you can't recognise the film by the backing paper the above suggestion will work fine. In fact if you got some DiXactol Ultra developer, use as a single bath, then the processing time for any type of film is pretty much the same. You really can put a roll of FP4 and a roll of HP5 in the same tank and get perfect results for each.