FileSelection: how add childern widget? how select a mask?

[Filip Hroch <hroch physics muni cz>]

Ciao,

I want add some childern widget to FileSelection dialog. I'm using 
a "wrong way", the nonportable feature with the main_vbox like:

...
  GtkWidget *filew;
  filew=gtk_file_selection_new("Save FITS file");
...
  b = add_entries(filew);                                                       
  gtk_container_add(GTK_CONTAINER(GTK_FILE_SELECTION(filew)->main_vbox),b);     
  gtk_widget_show(b);                                                           
..

Is there a possibility for this by a clean way (after upgrade to GTK2.0)? 

Version GTK: 1.2

thank you
FH