CascadingDropDownList and Control-Click

I have two CascadingDropDownLists in a search form, and I would like to give the user the ability to "control-click" an item to eliminate the selected item from the search results.

Here's an example: I have application, service and location DropDownLists on my search form. If the user selects an application, then only those applications are included in the results. If no application is selected, all a开发者_StackOverflow社区pplications are included. I would like to have the ability to control-select an item in the DropDownList and have that application not appear in the results. I have several other controls on the page, so space is limited.

Are DropDownLists even the correct control to use? UI design isn't one of my strengths.

I've posted a solution to this on my blog: http://codersbarn.com/post/2007/07/21/Code-Snippet-Cascading-DropDownLists.aspx

Hopefully this will help you out :-)