What about a double daily to DUB?
If it were to do the following it might work a bit better
BLK/STN
STN/BLK
BLK/DUB
DUB/BLK
BLK/GRO
GRO/BLK
BLK/STN
STN/BLK
BLK/DUB
DUB/BLK
Again not the greatest timing for DUB but it would allow a day trip with the first flight arriving into dub around 1020ish
Not sure how double daily would work from BLK (remember LS to BFS?) and it may just draw pax from the LPL & MAN services