How to modify Silverlight AutoCompleteBox commit behavior

Question

I needed to modify the AutoCompleteBox behavior slightly and Jeff Wilcox's excellent blog entry got me on the right track. I was able to use his example to modify the behavior so that it doesn't update the TextBox as the selection is changed, but I need to go one step further.

I need to modify the default commit behavior so that rather than simply replacing the text in the box with the value of the item selected, it should APPEND that text. Since the AutoComplete box is no longer a part of the ToolKit, but Silverlight itself, I can't find the source for the Selection Adapter and therefore can't figure out what method I should be overriding to affect this behavior.

Has anyone done this and can they point to the method(s) I will need to implement in my own class to make this behavior change?

Thanks in advance,

Steve