Your startup is worth 100.  So what is 51% of it worth?
aidenn0: If I want to give up control of the company but still keep part of the future profits of the company (which is basically what this question asks), it makes more sense to just sell to a public corporporation for a mixture of cash and stock.  This is basically the same idea.You get Money, give up control of the company, but also the rights to some of the future value generated by the company.  The waters are muddied a bit by the fact that the corporation has existing business that affects the dividends received, but in theory that's already priced into the stock by the market.