In OnBeforePopup you could detect that it is the form, and do either of these:
- block the navigation, then execute JavaScript to open the new window with a custom name like I showed you, so the parent - child relationship is preserved
- allow the navigation, but then execute JavaScript to re-write the page HTML so that you change the target name to FORM_2, FORM_3, ... for the next time a user clicks it.
Both of those only add a performance penalty at the time the user clicks to open a new window.