Hi,
Don't know if this helps you, i've been playing with thinstation for a couple of weeks now, with RIS running side by side. we are only trialing it at the moment and as such this was the quickest way i could work out.
The way i did it was to use the macaddress of the workstation and set up a dhcp a reservation with the thinstation image(thinstation.nbi) as option 67 within the reservation, leaving the scope options alone.
i am also using the machines GUID to 'prestage' it in the domain and boot a specific boot rom from rom-o-matic using the remote install server setting. i couldn't get the thinstation boot rom to boot correctly for some reason.
this could work as a long time solution if you are planning to roll out a specific number of workstations as thin clients.
hope this helps
dperrott