My question is how to set an add-in active for all users on a computer (XP)?

I have created an add-in and it is used by many users at our company.
But someties they want to use it on a different computer in a conference
room and then it does work even if the add-in is installed on the computer.
The user must activate it from the tools-addins menu.
However, most of these users never read instructions so I I want my add-in
activated when Excel is opened for every user loggin in to the computer.
Is there a solution to this?