Presuming the company fully owned (or with some sort of pro-rata split) you could tax the parent company for the total of their holdings. If they truly were separate companies, well, that satisfies the OP's objective too, no?

(Note I'm not a big fan of corporate taxes in general, I'd rather we not tax corporations and tax individuals more aggressively. Get rid of special rates for capital gains and have a much more progressive individual tax system.)