I have a (horrible) solution for that as well. Make the board criminally liable for the actions of employees, contractors, or other agents where such actions are a condition to the employment or contract.

Tax rates will probably need to go down and this is obviously just a thought experiment because no change is possible as we are too comfortable being hypocrites.

There is a much simpler solution for the vertical integration problem. If you buy something from another company which has already paid tax on it, you don't have to pay tax on it a second time. The resulting tax is called VAT.