Launching Excel add-ins

I can add new add-ins to the excel application using the add-in manager. However this means that all add-ins will launch whenever I start Excel.
I would like to create a shortcut with a target pointing to the *.xll add-in that I want to launch.
Before this works I am told that I need to make a change in the registry, but I do not know where.
Any ideas?
Thanks.