in window.c:
        { "ViewDualScreenPresentation", NULL, N_("Dualscreen Presentation Mode"), NULL /*Shortcut*/,
          N_("Run document as a presentation for multihead screens"),
          G_CALLBACK (ev_dualscreen_init) },

in my file:
gboolean ev_dualscreen_init(GtkWidget *widget, GdkEventCrossing *event, 
	gpointer user_data)
{
	EvWindow *presentation_window = EV_WINDOW (user_data);
	g_assert(EV_IS_WINDOW(presentation_window));