Single WP installation with NextGen to transfer to Multisite. But NextGen have issue with multisite

I am a web developer with lots of clients. I have single WP installation ( with 40,000 photos which all is managed by NextGen 2. I recently developed a Multisite ( which I transferred all my other client inside that multisite. Now I have issues with this since NextGen does not support Multisite and 40,000 photos is a lot to start importing again with different photo gallery plugin. So I am wondering is there any easy way to transfer this website into my Multisite and still have all the photos intact? Or should I just leave it as it is.