I'm not sure if there's a way to, but if you figure it out, be careful... especially if you plan on doing anything that could be considered working off the clock. It's unlikely they would find out, but it's not worth the risk.
workbench is entirely on targets internal network as far as I know so there is no way to access it from home unless you have a VPN connection into their network or possibly a DNS entry that would give you access to it
Only ETL and above can access it, through Virtual Office which is a Citrix application allowing them access to Target's internal network via any internet connected PC.