Sadly, no. The AF3+2 pants can only reduce the cost of a spell to 0 MP, they cannot make you gain MP. I was somewhat sad when I heard this too.
Printable View
Aw. Well that sucks. It wouldn't really be overpowered in either case, as you would only be able to do it like once every 8 minutes (assuming divine seal merits, but who's crazy enough to do that?).
Looking at the numbers again though, seems like Penury Cure5, Penury Cure5, Divine Seal Cure5 actually saves you 330 MP (assuming no overhealing), while combining a divine seal and penury (if it actually had worked) only would have saved you 278 MP, so it wouldn't have been a smart thing to do in most cases anyway.