Could you not use stages? A twinset and an AL80 of bottom gas should last you 2 mix dives. You can get this filled from your favoured cheap supplier before you go. If you only plan another 2 mix dives you can just get the twinset and stage filled up by the skipper.
It may be more slightly more expensive but:
you won't have to move J's around, or hire them or phaff
you won't have to hire a bigger transit,
you won't fall out of favour with the skipper,
he will blend the gas for you giving you more holiday
I know tech 1 dives who use the twinset and stage and deco bottle approach for diving weekends, particularly when gas is going to be difficult to find.
jd