Yes this is possible using the $wp->add_query_var function used together with add_rewrite_rule .
Here you have an example:
Passing and retrieving query vars in wordpress
If you want more help here is a cut from one of my old plugins:
function createRewriteRules() {
global $wp_rewrite;
$new_rules = array(
'(.?.+?)/(stenskott)$' => 'index.php?pagename='.$wp_rewrite->preg_index(2).'&ort='.
$wp_rewrite->preg_index(1),
'(.?.+?)/(bilclas)$' => 'index.php?pagename='.$wp_rewrite->preg_index(2).'&ort='.
$wp_rewrite->preg_index(1),
'(.?.+?)/(inbrott-i-bil)$' => 'index.php?pagename='.$wp_rewrite->preg_index(2).'&ort='.
$wp_rewrite->preg_index(1),
'(.?.+?)/(om-glas)$' => 'index.php?pagename='.$wp_rewrite->preg_index(2).'&ort='.
$wp_rewrite->preg_index(1),
'(.?.+?)/(kontakt)$' => 'index.php?pagename='.$wp_rewrite->preg_index(2).'&ort='.
$wp_rewrite->preg_index(1)
);
// Always add your rules to the top, to make sure your rules have priority
return $wp_rewrite->rules = $new_rules + $wp_rewrite->rules;
}
add_action('generate_rewrite_rules', 'createRewriteRules');
function query_vars($public_query_vars) {
$public_query_vars[] = "ort";
return $public_query_vars;
}
add_filter('query_vars', 'query_vars');
add_action('init', 'add_endpoints');
function add_endpoints()
{
add_rewrite_endpoint('ort', EP_PAGES);
}