Updating Sophos on SBS 2008 client PCs without internet access

Hello.

I am looking for advice on how I might go about setting up Sophos on a group of client PCs to a SBS 2008 machine that does not have internet access (nor do the client PCs) and keep them up to date. 

There will be internet access in the building but it will not be at all possible to give the server internet access.

Is there a solution to what I am looking for?

Thanks,

Ian