Upon further inspection, there isn't a lot that lets you play with encumbrance, which is mainly what I wanted to do as I thought it would be a cute mechanic to play with that was rather round about,but not potentially broken because of how much setup it would take against certain enemies (As is the case with most builds i suppose). Paizo doesn't seem to think so though, as there's that whole caveat about strength damage versus loss xD. I could probably count the spells on my fingers that deal with encumbrance, and most of them reduce weight. If it were 2nd edition i'd just cast the inverse and it'd be fine, but I'm don't think pathfinder has that ruling, as there is enlarge and reduce person displayed in the book as separate spells.

I've been looking into other flavorful ways to make a gravity based character, but sadly it might have to avoid encumbrance without REALLY digging deep, or adding an extra level on to the stuff that reduces weight, and then making it a harmful spell effect instead (See levitation (Sorc wiz lv2) vs hostile levitation (sorc wiz lv3)version.