There is no tax free conversion to Roth IRA.  The backdoor only lets taxpayers get around the AGI limitation.

Just about the only time when the distribution is nontaxable is if your client opened the one and only brand new traditional IRA and immediately convert that to Roth, assuming there is no gain or loss.

You may like to refer to §1.408A-4 Q-7, which refers to §408(d)(1) and (2) for the rules on income inclusion.