If you have a traditional IRA or traditional account in a qualified retirement plan there is a way that you can manufacture tax withholding late in the year that will apply uniformly to each tax quarter by default, essentially equivalent to retroactive estimated tax payments. You can take a distribution from the traditional account, have the majority of it withheld for taxes (some custodians limit you to applying no more that 99% to taxes), then complete a rollover of the enter gross amount of the distribution to a traditional IRA using the funds that you would otherwise be using to make the Q4 estimated tax payment. This would avoid the need to annualize. The only concern is that you are only allowed one rollover from a traditional IRA to a traditional IRA in any 365 (or 366-day for leap years) period.
Also consider any underpayment penalty you might have for state taxes. However, certain states treat tax withholding as paid when received, so there in those states it's not possible to manufacture retroactive tax payments.
