I'd still suggest sponsored magic from The White God... The staff was known to do some things other than water, explicitly... and the ability to have God pay a fate point for you once per scene, or take a consequence hit for you once per session (?!?) to enhance your magic would still be pretty powerful... I mean, sure, there's extra debt, but anyone who'd be even vaguely able to use it in the first place, would very very much be ok with being in spiritual debt to God.
As sponsored, it'd be more theme limited, and have some significant perks w/in that theme... You could even afford to leave the exact definition a little fuzzy (and decide the appropriateness of each spell effect the player describes), since Soulfire in the book is, too... but I'd say Divination and Conjuration would be strong... perhaps the perk would be that it can sometimes conjure the real deal, if available nearby (instead of creating an ecto-item, the staff draws a nearby substance together)... maybe conjuring at evocation's speed and methods for the snakes...
Sponsored Magic is -4, +2 for the item of power... so still a -2 item. Sponsored Magic has a cost break for anyone with Evocation or Thaumaturgy, so in the hands of someone with either of those, it could only cost -1... and someone with both, it might cost -1 and provide a further +1 to control and power with the sponsored magic.