Is there any way to create a sandox-specific shared secret for Apple App Store receipt validation?

I'm getting set up to do validations of App Store in-app purchase receipts from my server, and everything seems to be working fine, except I don't see any way to create separate shared secrets for Apple's Sandbox and Production environments.

I'd like the shared secrets to be separate so that I can safely put the Sandbox one in config files in code repositories, for unit tests, for example. I would keep the Production shared secret only in the config files in our Production environment.

I can't seem to find any way to do this. Am I just missing something?