Most Airlines that operate a dual base policy (the CAA are happy with dual basings providing the criteria is met) offer dual bases to "volunteers".
Clearly your friend is being "volunteered" on the back end of a job offer. If he lives in Leeds (1 hr 30hrs away from MAN) but a lot longer to BLK then this is where the problem starts. Unfortunately the onus is then on him to find local accommodation to BLK.
If he was already working for Jet 2 then he may have a leg to stand on.
Thomsonfly have dual based crews between MAN + LPL but they mostly live around LPL I think.