sharing sessions , cart and whishlist between multiple instances of nop...

i'd like to have multiple nop instances run separately but share the same database. i'll use sso to keep the user logged in in all instances .....
in other words, if a user adds a product to a cart on instance 1, then moves to instance 2 and adds another product to cart, i'd like the cart to him to see the same cart with all products added from instances 1, and 2.

is that possible ?

NB: instances running in different context but are on subdomains of the same main domain and all share the same database.