Can I use replication/mirroring to have a "Current" database and a "Full History" copy? I have a database that is used for current operations.  The amount of data is starting to get a bit to much for the applications using it.

Most of the data is older and is very rarely needed.

I am wondering if there is a way to configure SQL Server to keep a mirror of the original database, but allow me to occasionally purge out old data (and not have it purge from the copy).

NOTE: My database is currently SQL Server 2008 R2, but we will be upgrading to SQL Server 2012 soon.
Define the data is getting to be a bit much?  I've got clients with 1B+ rows in a table and no performance problems at all.

You could use SQL Server replication to replicate inserts and updates to a remote machine, but basically have it ignore the deletes.

Before I'd start looking at hacking together something like that I'd probably look at index tuning or query rewriting to see what I can do to resolve the performance problems with the queries that I've got.