1. Force Lavabit to provide their private SSL keys and route all their traffic through a government machine that performed a man-in-the-middle style data collection; 2. Change their software to subvert Lavabit’s own security measures and log emails after SSL decryption but before encrypting with the users’ public keys; or 3. Require Lavabit to install malicious code to infect their own customers with government-supplied malware.
It sounds like he already has the ability to comply with demands for information. I don't see where this new stipulation by them requires any meaningful change to his existing infrastructure.