Update Center issue: How to hide/remove items from the Available Plugins tab

I have a much simpler problem, you might have a quick answer for hence you now have been deeper in the Update Center code.

After upgrading my RCP app to Nb 8.2 (from 6.5!) I see that a few Update Centers are made available by default under "Settings" on the Plugin GUI. they are "Plugin Portal", "NetBeans Distribution" and "Certified Plugins".

I simply do not want those in the list of possible Update Centers ... any easy way to get them out ? I would expect to find such settings in some xml/settings file ?

B