Offering lump sums to people 20 years out of the workforce is playing with fire.
If the participant elected a straight life annuity in 1997 with spousal consent, would spousal consent be required in 2017 to switch the payment from a life annuity to a lump sum? Does your answer depend on whether the participant's current spouse is the same person who waived the QJSA in 1997? The participant may have been single then but is married now.
If the participant was married, was divorced, and remarried, it is possible that the consent of both the former spouse (if living) and the current spouse would be required. It would, without question, be required if the elected benefit was a joint and survivor form (with the spouse as of 1997 being the joint annuitant). Please don't tell me that people with joint and survivor forms would not be able to elect lump sums if people with life annuity forms could!
How can you make sure that the participant (and spouse, if married) completely understand the consequences of the election? The participant has been long retired and is advanced in age.
Can an election to change the payment form from a life annuity to a lump sum be made by someone with a power of attorney or guardianship or can such an election only be made by the participant (and spouse) themselves? If someone is living in a nursing home that has guardianship over the retired participant, any idiot can easily see that the nursing home being able to act to switch from a life annuity to a lump sum is fraught with conflicts of interest.
If it were up to me, the sponsor should bite the bullet and buy annuities, however much more they would cost. Making the offer should only be done after obtaining an IRS PLR that says it's OK.