1. Go to 'Administration > Site administration > Plugins > Activity modules > Manage activities'
2. Make sure all the modules are enabled (eye open)
3. Go to a course main page. Turn editing on.
4. Disable the activity chooser dialogue from 'Administration > Course administration > Activity chooser off'
5. Open the dropdown menu to add a resource and select URL
6. Add a URL with whatever settings you want and go back to course
7. Enable the activity chooser dialogue from 'Administration > Course administration > Activity chooser on'
8. Click on 'Add a resource or activity' and make sure URL is present under 'Resources'
9. Edit /mod/url/lib.php. In the function url_supports() replace:

    case FEATURE_MOD_ARCHETYPE:           return MOD_ARCHETYPE_RESOURCE;

with

    case FEATURE_MOD_ARCHETYPE:           return MOD_ARCHETYPE_SYSTEM;

10. Reload the course page
11. Disable the activity chooser dialogue from 'Administration> Course administration > Activity chooser off'
12. Make sure that URL is not listed in either the 'Activity' or 'Resource' dropdown menus
13. Enable the activity chooser dialogue from 'Administration > Course administration > Activity chooser on'
14. Make sure that URL is not listed when clicking on 'Add a resource or activity'
15. Make sure that the previously added URL resource is still visible and editable