Andrea's idea sounds pretty good.
I'll throw in another approach that may work for your requirements:
For all the read-only users, you could replace the shortcut to the Access application itself with a shortcut to a command script that copies the "master" .mdb file to a local copy, then opens the local copy to the user.
I sometimes use this technique for .NET Windows applications hosted on a network share since you can't run those things directly from the share (due to a security restriction imposed by the .NET framework).
Here's a Windows command script example:
FILE NAME: MyAccessApp.cmd
SCRIPT:
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REM "S:\" would be mapped to the share hosting the master Access database application
REM Copy master file from network share to client local hard drive
xcopy /y /s /i "S:\MyAccessApp.mdb" "%APPDATA%\SteelersRule\MyAccessApp\"
REM Open local copy of application
"%APPDATA%\SteelersRule\MyAccessApp\MyAccessApp.mdb"
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I feel your pain on this issue - I've dealt with it and still deal with it
Micah