I'm going to assume that you already put Exchange 2013 in the head of everything in terms of client access. Since the workstation is not on the domain, Outlook can't do SCP lookups for autodiscover. This means it's going to fail back to searching
preprogrammed well known addresses for autodiscover (ex. autodiscover.domain.com, www.domain.com/autodiscover, etc). So if you make sure the workstation can properly resolve autodiscover.domain.com to an Exchange CAS Server (I would have it resolve to a load
balancer that fronts my Exchange 2013 CAS Servers and let 2013 figure out autodiscover) and that the appropriate ports are available to the workstation you shouldn't have any issues (other than some password prompts, but that should be expected since the machine
is not a domain joined workstation).
Oh, one more thing, since this is not on the domain, I'm 99% sure that autodiscover is going to return the ExternalURL values for services, (outlook anywhere, EWS, OAB, ect.) you should make sure those resolve appropriately as well.