He presumably would have done so by relying on a special IRS "safe harbor" rule relating to the taxation of a service partner's receipt of such interests, but that rule emphatically does not apply to an interest when sold to a retirement plan, which is supposed to be measured by its true fair market value.
This rule can apply where there is a relatively greater amount of indebtedness in the U.S. than offshore, and net interest expense exceeds a specified percentage of adjusted taxable income.