Portal ROle Creation

HI,

Currently Portal Users can access "BEx Portfolio" iview (SAP Delivered) which is assigned to a Created Navigational role which is used to publish BW iviews.

One of the option in "BEx Portfolio" iview is users can create own folders and save book marks...

My requirment is to restrict users (some) by not allowing to create any new folders just access content in the folder

Ex:

User 1 (Power) allowed to create folder

User 2 (non power) not allowed to create a new folder just allowed to access content in the folder

How can i achieve this

I tried to create another Z roles and going to permissions assing the read permission for those iview and assigned the Z role to the non power user

BUT this is not restricting them to stop creating the folders...how can i a