That hp total could work, though you'd probably have to round up instead of down or institute a "minimum 1" rule.
What if we convince Shade to go for 2 spell levels per Con?
Those are all the symbiont rules from the FF, I think.
In that case, what about this?
Heal Host (Ex): In desparate situations, a vizier's turban can heal its host by returning some of the transfered Con. For each point of Con transfered, the host can choose to sacrifice one spell level and point of SR to gain 1 hp per 2 HD of the host (minimum 1 hp). However, the host must make a DC X Fort save for each point of Con used for healing; the transfered Con becomes permanent Con drain on a failed save.
That looks good to me!
Are we actually ready for skills and feats?
Wow...you did make progress!
I'd like to work in some Knowledge (arcana), too, but otherwise the skills appeal. I'd be satisfied with just stating Knowledge (any three) and leaving it up to the DM upon which areas they'd like the turban to philosophize.
That quoted passage suggests more a lack of Spellcraft than Arcana.
Let's go with (any three).

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.