...BTW, there's an interesting variation on this method that uses a Roth IRA... Do your normal Roth conversion and withhold whatever amount you want for taxes. Then repay that amount into the Roth within 60 days from taxable funds. This achieves the same result, but has one distinct advantage... it is not subject to the one-rollover-per-year limitation since it is a conversion.
In case anyone revisits this thread, this last paragraph apparently does not work. After I transferred the amount I wanted from my tIRA to my Roth, I wanted to pay the taxes with after tax funds. I tried, both on line and with a Fidelity representative. As rayvt mentioned in another thread, there is no way to withdraw funds from a taxable account with withholding, which is what the first Fidelity rep incorrectly told me...
It was explained multiple times in this thread that you cannot have tax withheld in conjunction with a withdrawal from a taxable account. What's more, that's not at all what I described in the last paragraph you quoted, which involves withholding from a tIRA in conjunction with a Roth conversion. What I described in that paragraph is absolutely do-able, with all the mechanics having been discussed in this thread.
...There is also no way to move money from an after tax account in to a Roth without it being considered a contribution. When we did it from a tIRA, it was easily categorized as ROLLOVER...
Also not true. In post #54, cathy63 posted a link to a Fidelity deposit slip. Using that slip, you can transfer money from a taxable account into a Roth IRA and code it as a 60-day rollover, or a Roth conversion. You can also call in and have a rep do it for you.