CRM 2011 Custom Activity Ribbon customization

I've read this article about customizing a custom Activity ribbon.

I want to disable all the activity related buttons (task, email, phonecall, etc.) when the Homepage grid displays for a CUSTOM Activity entity.

I'm using Ribbon Workbench.

1) So in activitypointer entity, I have created an Enable Rule with a Custom JavaScript Rule that has a CRM Parameter of value PrimaryEntityTypeCode (etc).
The JavaScript will return True only if the PrimaryEntityTypeCode refers to a core Activity entity.

2) Then I created a Command that I have associated with the Enable Rule I created in 1).

3) Finally, I selected this command in "Behaviour/Command" of each button I wish to disable for a Custom Activity entity.

Well... it is not working!

Am I doing something wrong?
Does the article above only refers to custom actions added to the activitypointer ribbon or should it work also for the out-of-the-box buttons?

Thanks of your input.

Frank