Architecture question - relating three separate tables

I am using the aspnet membership and roles to manage security for my web application. What I'm wondering is how can I tie these three tables together so that when I have a user log onto their specific homepage, it will look up information on the tables egw_addressbook and ewise_device. Would I be best to create a column aspnet_id on the egw_addressbook and ewise_device or to create a table to tie these vars together, what would be the best way? I can't do anything to the my_aspnet_users table because if I alter that table the schema blows up and I get a nasty error that won't allow users to register.

egw_addressbook
         -contact_id

ewise_device
         -device_id
         -contact_id

my_aspnet_users
          -id 
A ...