Anyone needing the same thing (sidebox on non-ssl pages only) try this, it worked for me.

in
/includes/modules/sideboxes/sideboxname.php
(where 'sideboxname' is the name of your sidebox)

just replace this:
// test if box should display
$show_sideboxname = true;

with:

// show only on non-secure pages
switch ($request_type) {
case ('SSL'):
$show_sideboxname = false;
break;
case ('NONSSL'):
$show_sideboxname = true;
break;
}

The box will show on non-SSL pages only.