You're asking possibly two questions:
1. Can I open a database with a specific workgroup information file without using the command-line option?
A: Yes, first create the appropriate workspace and then a database under that workspace. Code:
Dim ws as Workspace
Dim db as Database
set ws = DBEngine.CreateWorkspace("location of .MDW file", "username", "password"

set db = ws.OpenDatabase 'etc
A2: You can open a database in exclusive mode with your current workgroup. Say you log into your database using your special shortcut and login. Close the database without closing Access. Now re-open the database using File->Open, and choose the "Exclusive Mode" option. This will open the db in exclusive mode, with the correct workgroup.
2. Can I open a database in exclusive-mode from the command line?
A: Yes. From the Access 97 help file:
/excl Opens the specified database for exclusive access. To open the database for shared access in a multiuser environment, omit this option.
So just add "/excl" to the end of your shortcut's command-line arguments.