Right-click read-only DWG in Windows Explorer?

I am looking for a way to add an action to the .DWG file-type, such that
I can use the /b command line switch and some piece of script to allow
me to right-click on a DWG and get an "Open read-only" option.

So the action should look like this:
"C:\Program Files\Autocad 2000\acad.exe" /b "C:\readonly.txt"

right?
But now what should the script in readonly.txt look like?
I have explored a couple of things, none of which are working for me:
"DBMOD 0" etc.

Any help would be greatly appreciated on this.
Thanks,
Josh.