How can Congress prevent bureaucracy firings?

Let's assume SCOTUS rules that the President can fire anyone in the executive branch at any time for any reason, what could Congress do to prevent it? Could it move parts of the agencies to the legislative and judicial branches? For example, could it create an office of special counsel within Congress to investigate the executive branch? Could it move the judicial portions of the SEC and NLRB to specialized courts where the judges serve for life?