I'm not as familiar with the homebrew versions, but there are plenty of uses for Reserve feats to function as bending mechanics, and by 5th level you can have spells known enough to qualify for at least one or two. The force-effect and air-effect ones can be combined in an Air bender with spells being more complicated and difficult techniques. A Water bender with Cold and Water reserve feats could also work very easily. Fire is a little more difficult as a 'caster since there's only the one reserve feat, but there is also the Swordsage (Desert Wind school is all fire all the time, as well as having a more martial-artist type focus, maybe slipping Diamond Mind in; "Fire needs focus, Focus needs fire.") and the Pyrokinetcist PrC via Psionics if it's allowed.

Earth Elementalist might work okay with a mix of Stone Dragon maneuvers as a Swordsage along with Setting Sun for the earthly control, along with dips in Warlock for the dirt-and-stone hand invocation and replacing eldritch blast fluff as rocks being lifted and tossed (maybe switching to Bludgeoning damage, but keeping it a touch attack.)