As a DM I would probably allow that at lower levels, but as ability mods can range from 30-50 I think I'm still going to omit it. But I do thnk at lower levels that may work. another approach that some official material takes is to give one spell every few levels such as to give a few of up to some level, and more up to a higher level, and so on as you progress. I believe dread necromancer does this too... in the end though it is your class, so I don't want to commandeer it (especially without a clear idea of where I'd point it )