Ad function to existing Wordpress plugin

What existing plugin do : Plugin show exit popup (standard browser exit dialog) always when visitor want to close page or want to go on other domain ([login to view URL]) What I need to add : I need to add a control of some domains which will be excluded from popup. It means that i will write somewhere that [login to view URL] is excluded and popup will not show if visitor go from sit to [login to view URL] but will show at all other domains + web close. Plugin in attachement