The problem will be that by default the Calibre User configuration information is stored at the user level. To achieve what you want, you need all users to use the same configuration information. This can be done by setting the CALIBRE_CONFIG_DIRECTORY environment to point to where Calibre should find its configuration information.
One way I can see to achieve this is to use a script/batch file (you do not mention what OS you are running) to launch Calibre. If you look in the resoruces sub-folder of the Calibre installation location there is a batch file called calibre-portable.bat that shows how the location of all the files used by calibre can be excplicitly controlled. The batch file is extensively commented so it should be reasonably clear how it works, but feel free to ask questions on anything that is not clear. The batch file supplied is for Windows, but the principles would apply regardless of the OS.
If you are running Windows and the configuration information is all you want to control then instead of using the batch file you could instead simply set the environment variable at the system level by:
- Go to Control Panel->System
- Select Advanced System Settings
- Select Environment Variables
- In the System variables at the bottom select New
- Set the name to CALIBRE_CONFIG_DIRECTORY and the value to the name of a folder to be used to store the Calibre configuration information
Make sure the location is a folder that has read/write permissions for all users. You will have to reset up the settings the next time you use Calibre and re-install your plugins as it will act as if it is a new install, but this time they should now apply to all users.
In theory it would be possible to initially populate the chosen configuration folder with the settings for an existing user by copying that users existing configuration (its location is available via Preferences->Advanced->Miscellaneous) but I think that plugins need re-installing if you do so.