Answering your actual question, yes, you can spread out the estimated payments.
The IRS assumes that 1099-R income is earned spread out over the year, so they will want to see the payments spread out over the year. When you make a conversion at the end of the year, this assumption hurts you because the IRS wants to see the taxes paid in all 4 quarters, not just at the end of the year. But if you make the conversion in the beginning of the year, this assumption works in your favor. You can spread out the tax payments over all 4 quarters (and possibly invest the rest in the mean time) and not incur a penalty.
Of course, you may need to include estimated taxes for any other income, and I have not talked about tax brackets or IRMAA. If you are married filing jointly, and you have no other income, you can convert about $100,000 and stay in the 12% bracket. Converting more will push you into the 22% bracket. You might want to spread the conversion out a bit.
