Hi

Two questions:

one workgroups ability to access it's server, so that might not work
The overkill method is not the method I would choose, but I do not understand
why this should happen. The workstation and server services are still running.
By an explicit configuration, you should still be able to access all ressources.
The computer browser service just maintains an updated list of computers on the
network and supplies this list to computers designated as browsers. If this service
is stopped, this list will not be updated or maintained[1]

Setup a scope ID.
This is a solution, but then that workgroup will be completely isolated from the other
machines (outgoing and incoming), I think. It this what you would like to achieve?
I thought you simply want to have vanished the machines from the network
neighbourhood.

Cheers.

[1] http://www.theeldergeek.com/computer_browser.htm