windows - How do I give a machine read access to a share when there is no domain?

I have server A which is a windows 2008 box that runs standalone (not part of any domain).

I also have server B which is part of a windows domain.

Server A is a file server sharing out a directory.

How do I allow server B read access to a share on server A?

If both machines were on the same domain I would simply right click the share go to Security and add the machine account as read only. It would be found in the domain directory.

But if I try this in my scenario, server B is unknown so I can't grant it read access to the share on server A.