One important point you are missing, with all due respect. The IRS has said in some of its discussions on the issue that the reason you can use seasoned money is that it constitutes a distribution (and so the entire premium is taxable). (The concept of "seasoned money" is that it is distributable at the participant's election.) I don't know if this is their current position ... it's been a long time since I discussed insurance in a plan with the IRS .... but i would at least warn the client that the IRS could take the position that the payment of the premium is taxable income. In any event, you need to be sure your plan document permits seasoned money to be distributed, or this option doesn't work.
Three more things: first, the 49.99% is applied on a cumulative basis in a DC plan. So, you add up all contributions for all years (up to the year in which the premium is paid), take 49.99% of that, and that is the total premium that could be paid and still have an incidental death benefit. So, you may have more "room" than you think.
Second, don't forget that, even if you take the position that the premium payment is not taxable income, remember that the term cost always is. And, the amounts on which taxes are paid becomes a basis if the insurance policy is distributed to the participant.
Last but not least, the provision of insurance is a benefit, right, or feature, and cannot be discriminatory. If it has not been offered to other participants, you have a problem that needs to be repaired, probably through VCP.
Best wishes for a likely big mess!