Umm, that seems not a smart idea to me. Yes, the Eldritch Master could be a solution. I've only heard of it, never read it, but it seems to me that it shouldn't be able to full spellcasting progression in another class, at least not while adding more spellcasting levels to your current one.
Quite frankly, an evoker who could dish out fireballs, explosive cascades, flying, haste, polymorphing and healing would be overpowered. I mean, why not add fighter feats, better hit points, sneak attack, and 8 skill points a level. (I'll ignore the obvious cleric joke)
Essentially, you could get the Eldritch Master (which I don't think allows for that powerful of spells) or multiclass to cleric. Anything else would be overpowered.