How can I add my live application to Environments without wiping out all production data?

So I have been developing a custom application for a small business for about six months now. We have done a soft launch as we continue to test and improve the application. I am realizing more and more how much I need a development/testing environment so I can improve the application without affecting the end users.

Unfortunately, I didn't START the application's development using Creator's Environment feature, so I only have the one production application.

After doing a test, I found that adding an application to Environments will wipe out any existing data in the application. Since the client is already using the application, I would not easily be able to do this.

Any suggestions or workarounds? There is very little documentation on Creator's Environments, making this problem a little more uncertain.