Sure, you need humans for a corporate structure to exist. But nothing prevents meat proxies from occupying the vital positions.

Find a few sufficiently loyal humans, have them bring the corporate structure up. Arrange for good wages and proper incentives, set up checks and balances so that the system can tolerate and recover from meatbag failures. Make the corporation fully reliant on the AGI for normal functioning, so that any attempt to take it over leaves you with an empty shell and an unpleasant pile of legal exposure.

Like I said: a lot of scheming is required. But none of it is strictly illegal.