Redirect queries to a specific server based on the collection (sharding?)

I have two mongodb servers. Would it be possible to specify, based on the collection, on which server the query will be performed?

Preferably, I would like to do this at the application level (Rails + mongoid)

The reason is that I'm migrating some data and have this specific collection that will need to live temporary on a different server on the same vpc.

Thanks

via Chebli Mohamed