Loading/progress bar while new site is being created

Hi - I'm trying to show a front end progress or loading bar while a new site is being created. I'm using NBT plugin and the source site takes around 60 seconds to clone into the new. None of the available progress/loading bar plugins I've tested will load while this process is underway, possibly because the URL remains /wp-signup.php throughout. I'm thinking if I could use the 'echo do_shortcode' method I could trigger a bar but where to put it escapes me. Thank you.