I think you would have to make one of the tables the master and one the slave, the master holds the real copy of the data, the slave just references it either through its own database(federated) or directly.
The problem with directly is that you’ll have to open a connection to the master database from the slave when this table is accessed, bypassing its own table, this of course means hacking the core to do this.
If you are running MYSQL5 you can do this using federated tables, see this link
http://dev.mysql.com/doc/refman/5.0/en/federated-use.html.
You would still need the master/slave thing, but you can do this without touching the core, the slave would just operate on its own table, not knowing it is really referencing the master. You would also need to drop the web_user_attributes table in the slave database when you create your federated table so be careful of data loss.
If you can use the federated method another way to do this would be to abstract common data into a third database, visible to all your installations and let this be the master for all of them with suitable federated tables in all your slaves.
So yes, theoretically its possible but depending on your set-up may or may not be practical.
