Methods are not supported at ListPages. It’s due to fact that, List pages are supposed to be deployed on EP as well as on Rich Client.
Now, for your problem if you have button that is supposed to be run at Rich Client only, you can set DisplyTraget=Client and you can override methods. If that button is mandatory to be used at EP, Consider replacing your button with a menu item and that menu item will be calling a class. Let your code be in a class. A separate class than Interaction class.
Additionally have a look at my blog post, if that can help you.