In no minimum IP leagues, one of the best "alternative" strategies is to do what you've done - go with all relievers.
BTW, any league I joined where the commissioner changed the rules AFTER I drafted would be a league where I'd be demanding my money back (if I paid) or possibly even consider dropping out. Changing the rules like that is a heck of a lot more unsporting than using an alternative (but valid and viable) strategy.
As for solutions, maybe trade two closers for mid-level starters with solid ERA/WHIP numbers. Those two should give you at least 12 IP a week, leaving 13 for the other 7 guys - and most relievers average 2+ IP/week. Or cherry pick a solid two-start pitcher (if any) each week. But, the last person I'd trade with is the commissioner, that's for sure.