[Plugin: Post Notification] share subscribers on multiple installs (same db)

hello, i have 2 wordpress installs on the same database. i did this so they can share users (via the users table). i have the email notification plugin installed on both wp installs. i would love if the 2 installs could share the same email notification subscribers. is this possible? any help would be…well…helpful.

http://wordpress.org/extend/plugins/post-notification/