I like the way you link government to corporations. The link is concentration of power: huge financial power or force/law monopoly.

I would like to add another consideration:

[corporations] can use their money to create a government to better serve their interests, not the interests of the common person

Funding of political parties / candidates is the key here.

Big corporations don't vote, but they give big money to congress members, presidents, etc. This could be banned. Just fund politics with private individual donations - establishing a maximum donation amount per person, otherwise it's still plutocracy.

1 person = 1 vote ---> 1 corporation = 0 vote
1 person = up to $ XXX donation ---> 1 corporation = $ 0 donation

It would be hard to make this happen because funds would go down a lot, but campaign are expensive for politicians, and lobbies are very powerful right now.

How do you enforce a law of this kind without giving the state more power over corporations?

I think the fight of power vs power is way better than the fight of power vs powerless. So corporations vs state it's better than corporations colluding with state (against citizens will).