Can I sign in to multiple iCloud Drives at he same time on my Mac?

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multliple iCloud Drives ?

I have two iCloud accounts - one for personal use (primary account), and one for shared use with my business partner. I would like to use the iCloud Drive associated with the secondary business account to share data, files and folders with my collaborators. It would be possible to sign in to my business iCloud account via a browser and access the iCloud Drive associated with it, but this is laborious. The mac does not allow sign in for more than one primary iCloud account, so I cannot see anyway to access/load the business iCloud drive onto my mac.
I have just updated to Yosemite.