Currently, the procedures some executive agencies, e.g., the Social Security Administration, the Internal Revenue Service, the Dep't of Labor (carrying out ERISA) do not treat same-sex couples the same as opposite-sex couples. These agencies make it harder for opposite-sex couples to attain marital benefits than same-sex couples through, e.g., the SSA looking to states to determine marital status.
The Supreme Court, in United States v. Windsor, held that the federal government cannot define marriage so as to discriminate between same-sex couples and opposite-sex couples.
The Executive should order his agents carrying out this decision to "immediately make compliant with Windsor any procedure or policy which will cause same-sex couples to forfeit benefits afforded to opposite-sex ones."