An additional thought with regard to this. I would expect that for distributions from the 401(k) that are not made in the form of annuity would mean providing the payer with Form W-4R, not Form W-4P. The instructions for Form W-4R define periodic payments as those received in "installments." I don't see how RMDs could be considered to be amounts paid in installments since the distribution is not restricted to the just the minimum required.
