Actually - wasn't there a pretty popular homebrew class called the Blue Mage or some such which had that be its schtick?

One minute... *scrounges on Google*

Well - apparently there are several 3.x homebrews called "Blue Mage" - but this is the one I was thinking of - Blue Mage

Basically they're a sorcerer variant which learns spells by experiencing them. Not quite what you were looking for - but might be a good baseline.