5 C.F.R. § 630.1706
(a) If an agency determines that an otherwise eligible employee who could have made an election during a past period to substitute paid parental leave (as provided in § 630.1703) and enter a work obligation agreement (as described in § 630.1705) was physically or mentally incapable of doing so during that past period, the employee may, within 5 workdays of the employee's return to duty status, make an election to substitute paid parental leave for applicable FMLA unpaid leave under § 630.1703(a) on a retroactive basis. Such a retroactive election shall be effective on the date that such an election would have been effective if the employee had not been incapacitated at the time. Consistent with § 630.1206(f)(4), this retroactive election must be made in conjunction with a retroactive election under § 630.1203(b), if the FMLA unpaid leave was not already approved. As part of such election, the employee must agree (in writing, as described in § 630.1705(b)(1)) to meet the work obligation or pay the required reimbursement (if applicable) unless—
(b)
(1) If an agency determines that an otherwise eligible employee is physically or mentally incapable of making an election to substitute paid parental leave (as provided in § 630.1703) and entering into a work obligation agreement (as described in § 630.1705), the agency must, upon the request of a personal representative of the employee whom the agency finds acceptable, provide conditional approval of substitution of paid parental leave for applicable FMLA unpaid leave under § 630.1703(a) on a prospective basis. The conditional approval is based on the presumption that the employee would have elected to substitute paid parental leave for the applicable FMLA unpaid leave and would have entered into the work obligation agreement if the employee had not been incapacitated. Within 5 workdays after returning to work, the employee must enter into a written agreement to meet the work obligation described in § 630.1705 or pay the required reimbursement (if applicable) unless—