It is not really so difficult.
Because investors are a diverse group, they rarely get together on their own to force corporations to take specific actions. Thus, the power of investors to enforce change is ignored.
But, investors have another power that does not require concerted action--they vote with their feet, and, if the appropriate "force-fields" are erected, the sum of their individual actions will, in a way that would have pleased Tolstoy, change corporate behaviors.
First, the Congress and administration needs to establish some definition of "excessive." Let us say that it is total compensation in excess of 30-fold (or 25-fold, or 65-fold, or some other number) the average worker in that firm, or some higher multiple of the lowest quintile, or some other number. Something. This would be the major argument, but something can be agreed. It will be some number.
Once that definition is established, the only remaining step is to disallow capital gains treatment for investors in companies that do not meet that standard.
Investors will vote with their feet. They will tend to put their capital into companies whose compensation practices will allow investors to get the capital gains preferences. They will tend to take their money out of companies that pay excessive compensation according to the defined standard. Share prices of the non-conforming companies will go down and their cost of capital will go up.
On the other hand, if a company has a truly spectacular CEO, whose benefits to the company more than outweigh the tax rate differential, such as Steve Jobs, investors may invest anyhow. It would be a good measure of just how valuable a person really is.
Moreover, since investors do come together once annually to elect the Board, it is highly likely that they will sack a Board that paid excessive compensation and thus denied them capital gains treatment for their gains.
No regulation or regulators are needed. The company will have to state in the Annual Report, audited by outside accountants, that the compensation does, or does not, meet the standards. It would be part of normal reporting. Misreporting is actionable as fraud..
Note, under this proposal, the government is not telling companies what to do, but rather erecting a force-field and allowing them the choice. Force-fields permeate our tax code and government policy, and are often much more effective than regulations. Deductibility of interest rates on mortgages created (long before the bubble!) a nation with a high home-ownership rate. Title to land for working it helped settle the West in the 19th Century (Homestead Act).
Finally, if the definition of "excessive" is tied to some multiple the average worker or lowest paid quintile, the impetus for off-shoring is reduced because the major reason for doing so, to take advantage of lower wage workers, compromises the total compensation that the top people can get and still allow their investors to enjoy capital gains tax rate.
Not a bad dilemma for corporations to have to handle.
It is a "creative tension." Creative tension is good.