How To Hide A Specific Category From Parametric Search?

Hi,

I see a similar question here but can't seem to implement it:
http://wp-types.com/forums/topic/how-to-hide-a-specific-product-category-from-parametric-search/

I'll re-iterate the question:

1 – Set up a basic parametric search with a dropdown for categories.

This normally lists ALL categories. But I need to remove some hand selected ones from the dropdown list. Caridads solution as far as I can tell doesn't all me to keep it as a "Set value by URL parameter" which is needed for a parametric search, no?

Any solutions?