The simple way around this is to write something that injects the variables into the project scope. This function will read all the variables from the url and inject them into the project scope. You should never rely on register_globals, but if you don't want to update old code this is an easy workaround.
function register_globals()
{
//if register_globals is on then return
if(ini_get("register_globals")) return;
//inject URL vars into scope
foreach($_REQUEST as $key=>$item)
{
$GLOBALS[$key] = $item;
}
}