What you are asking is possible. You could take the action log entries older than x days and move them to another database, or another table, then create a view that covers the tables from wherever you put them and just query the view ( select something from viewname ) as opposed to the table name.
Now the above scenario is VERY generic, you could put the table in another DB, in the same DB, another server with another DB, etc, but it gets complicated to maintain DB aliases and linked servers, security and such...
I understand the want to keep action log stuff for a long time, but the need isn't there in my opinion. Personally I backup the DB once a week, trunc the action log table once a month and if need be, restore to look up action log items.
As for the DB, you should be focused on access times, and access methods rather than data size, storage is fairly cheap these days ( depending on your hosting solution of course )