you could take it out in dribs and drabs and put into a regular brokerage account which he could use until depleted, no time limit. Or, as recommended, funnel to a trust where he is bennie, no tax shelter rules.
having to take money out of an IRA is not the same as having to spend it. I don't think it is tragic to have to remove money from an Individual Retirement Account if you weren't that Individual. The money doesn't vaporize, it just comes out of tax shelter. I see no problem with inherited IRAs only being allowed to go on for so long. Presumably, persons wishing to leave inheritance have more than tax shelters to pass along. That is of course the way to avoid rules about inherited IRAs.
Gets complicated to figure out how to look out for a loved one from beyond, but perhaps finding the right fi advisor to assist when you no longer can? I have nothing like this situation but very interested in what your plan ends up looking like. Smart people find a way, and that is absolutely you, Vaca.