For starters, the literal '\\HOSTNAME\Joe' results in the string \HOSTNAME\Joe. I don't think that's what you meant to use. Don't forget to escape your backslashes! To get the string \\HOSTNAME\Joe, the literal would be '\\\\HOSTNAME\\Joe' or the "optimized" (and confusing) '\\\HOSTNAME\Joe'.

But I'm not convinved that would help. If it's 'DOMAIN\bob' for domains, wouldn't it be 'HOSTNAME\Joe' for local accounts? I'd also try just 'Joe'.