Discarding Tags

I've looked through the config settings and the -help option, but I really haven't found what I need...

Since I'm using ASP.Net - is there any way to set Tidy so that it will NOT discard tags it doesn't recognize, but it will still Tidy what it does recognize?

As it is now, if it's not in the config file, it totally deletes it from the page.

David Wier