Ummm . . . I have a 'kind-of' answer to my own question . . .
In the PHP file ' main.php ' ( in the lib/template folder) ,
I added the line
$showSidebar = 1 ;
after the existing original code:
$hasSidebar = page_findnearest($conf['sidebar']);
$showSidebar = $hasSidebar && ($ACT=='show');
I now have a sidebar, with menus, on all pages. Not ideal, but a big help.