Leaving an “insurable interest” annuity might be an option. It differs in several ways from a spousal survivor annuity, however.
First, you must demonstrate at retirement that you are in good health as demonstrated by a current medical exam.
Second, you must submit affidavits supporting the assertion that the person you name would benefit financially by your continuing to be alive, unless that person falls into one of the categories where such a relationship is presumed.
Third, the annuity is based on 55 percent of your unreduced annuity (in contrast to the 50 percent maximum under a spousal annuity for FERS) and is reduced by a percentage that depends on the difference between your age and the age of the person you name.
See Chapter 3, Section 4 in the Federal Employees Almanac for details.