customize Content Type Dialog box

I want to customize the Content Type dialog box that comes up when you upload a document.  I want some of my columns to show as read-only.  I don't want to set these columns as hidden, as we still want to be able to see them.  But I have them defaulted to a certain value, and only want them to show as read-only when users are uploading a document.

Anyone know how to do this?

thanks!