In order to force an install on 7.0, editing checkinstall.php did nothing. Instead, you can just remove the following lines from install/includes/'Installer.class.php':
if($version[0] != '5') {
$noerror = false;
$type = 'error';
$message = 'You need PHP 5 (your version: '.$version.')';
} else {
$type = 'success';
$message = 'OK! (your version:'.$version.')';
}
Also, it will throw an error upon completion.. Just ignore it, it seemed to install fine.