sharing DBs between 2 instances on same box without linked servers

[siddhath]

All,
I have two databases A and B on one pyhsical box called 'P'. I need to put
another instance of database A on same box. i can not have same database name
twice on same physical box twice so my solution was to create another
instance of sql server on same box and create database A on it. so now it
looks like this.

Physical box P has two DBs
-A and B

New instance of sql server on same physical box P has
- A (copy of DB A )

Both DB's "A on physical box P and A on the new sql server instance" need
to share/join to single copy of B runing on physical box P. Is there a way to
do that without using linked servers?
Thanks
Siddharth