There must be a major reason why KLM chose not to return to BFS and to instead to fly to BHD, because from the outset KLM made it clear that if the route was successful they'd add a second daily flight.
BHD generally has 9-10 departures 06:30-07:15 using overnight-based aircraft, hence the slot restrictions. However, it would be possible to use gates currently used for 07:15 departures for both a 06:30 and 07:15 departure by a) bussing passengers from the gate to the aircraft parked on the apron to the west of the terminal (I've seen this before with a few Aer Lingus flights) or b) towing the aircraft from the apron to the gate after the first flight has departed.
BHD management need to do all they can to keep KLM at the airport, because the airport has essentially reverting back to its network of 5 years ago when it was just Flybe plus a link to Heathrow.