This question also references:
Me and a fellow user (in the question referenced above) want to use a custom widget on a custom plugin page without having that widget appear in every "position on all available pages". Interestingly when we both create a plugin page we cannot exclusively feature a plugin on a custom plugin page. It appear that the array $templatelangkeys defined in qa-page-admin-widgets.php (that contains the avaliable pages a widget may appear on) does not automatically update when there is a new plugin page avaliable. This can be demonstrated when trying to add a plugin widget to a plugin page under admin -> layout -> add widget - the plugin page simply isn't avaliable.
My question: Is there a method to add a plugin page to the $templatelangkeys before it is rendered on Admin -> Layout -> Add Widget under: Show widget in this position on the following pages?