using RSA-the-cryptosystem to secure RSA-the-company's patent?

Apropos the recent thread on tamper-proof programs... Can anyone think of a way that RSA-the-company could include some sort of RSA-cryptosystem-secured check in a release of PGP so that it would only interoperate with other versions that have the same check? I don't see how it could be done, but it's sure an intriguing idea. --- Jef