The simplest way would be for him to say, "hey, I'm never going to buy ads on my own site, so don't let anyone impersonate me." If Zuck wants to tell us something on Facebook, he'll just put a banner at the top of our feed. Or if he does want to run ads as himself, he'll pull some other founder-fiat move. Keep in mind the engineering motto of the company we're talking about. They don't need to stick to the rules.

Corporate boards usually have controls against appropriating company resources for personal use.

Presumably there is a tax implication too? In the UK this would probably be a benefit-in-kind and taxed say it's market value as income.

Yes. Same in the US. Things like private jet use are applied as income. However, I'm not sure you would have to do so at retail rates. For example, you would have to pay taxes on the cost of the private jet use. The marginal cost of something like running your personal ads on the favebook platform is so low as to probably not be considered "material" by the tax man.

Considering he controls 60% of the company, such controls are meaningless.

The controls would be something agreee to as part of taking the company public or some stage of auditing.

Owning a controlling stake doesn’t mean you can fiddle around with every corporate asset at your whim.