There are plenty of tricks and methods to get (partial) spontaneous casting onto a Wizard (Alacritous Cogitation, Uncanny Forethought, Proteus, Spontaneous Divination etc.). How about the Archivist?
The easy answer is play a Favoured Soul, Mystic or Generic Spellcaster instead, but I really like the chassis of the Archivist, and it's potential to learn the vast majority of spells from all class lists.
Spontaneous Healer and Spontaneous Summoner come to mind, but are very limited.
Cheers - T