There are a couple of ARFs you could exploit to get your CL back on certain spells, like Stonesinger, Lightbringer, Pyromaniac, Arcane Training and Wanderlust, and probably some feats but I'm no expert on PF CL boosting by any means. This is just one of those cases where Paizo shows their contempt for multiclassing.

I'll see if I can get some of the core feats up and color-graded tomorrow, as I should have some free time then.