MarketPress Add to Cart button fails to function with FORCE_SSL_ADMIN

If the user browses on HTTP and FORCE_SSL_ADMIN is turned on, there’s a problem with [mp_buy_button].

var ajaxurl = ‘HTTPS://server/wp-admin/admin-ajax.php’;

This will violate same protocol security policy and Add to Cart will simply not work.

Is there a workaround for this?