How to remove Delegate button from a notification

Hi,

I am working on iSupplier Portal. Currently the Acknowledgement Required notification goes to our suppliers with Accept/Reject/Delegate options. We want the supplier user to simply accept or reject the Purchase Order, no delegation allowed. When clicked on this button, the user can see a list of all employees, groups etc which obviously we don’t want to expose to outer world.

How do we remove the 'Delegate' button from the notification? We want to minimize customization/extension. I tried personalization but there is no option to remove/hide the 'Delegate' button. Can it be done using some profile option? The "WF: Notification Reassign Mode" is set to delegate at site level. The other options for this profile option are Reassign and Transfer. If they had an option such as 'None' for this profile, I could have used it for the iSupplier responsibility