There's no good way to do this with ClickOnce. ClickOnce apps are installed under users profile folders. What should show up on the dashboard if one user on the machine has it installed and another user doesn't?
You can write custom code in your app to create the registry entry, but if the user doesn't have security to create it your code won't either. A second problem with that approach is deleting the registry entry when they uninstall.
I think it comes down what's important. Can you switch to an .msi? Is losing the auto-update of ClickOnce a big deal or not? If you have to stick with ClickOnce, you'll have to find a manual work-around. This article is one approach to solving problems like this.