How can I "archive" mails in Mail App to another internal drive/partition to save space but still have it searchable in spotlight (and preferably visible, searchable, draggable in Mail App)?

How can I "archive" mails in Mail App to another internal drive/partition to save space but still have it searchable in spotlight (and preferably visible, searchable, draggable in Mail App)?

Background:

I am using Mountain Lion and Mail App and running out of space on my small primary SSD drive (where I keep OS, apps, key user preferences/data and mail for speed). The mail data is the big variable (many GBs) and I want to "archive"/move some of the old mail to my 2nd drive inside the Mac. But I still want it searchable inside spotlight and preferably even inside Mail too. And I'd like to be able to still drag and drop old mails into this archive folder.

What I've tried that seems to work:

This seemed to work:

1. Move the archive folder/mailbox to the 2nd drive/partition/folder (don't delete anything inside Mail App)

2. Create a symbolic link from its new location to the original/old location

This seems to work, it looks as "normal" and as if nothing happened inside Mail App but the folder now resides elsewhere and seems searchable etc. But I'm not sure that once caches refresh or over time with updates etc if stuff will break horribly or corrupt.

Is that the right way to "archive" mails in Mail App to another internal drive/partition to save space but still have it searchable in spotlight and visible, searchable, draggable in Mail App?

Thanks in advance!

Cheers,

Daniel