In the CloudBank, set NbrTracks to 1. Then select the track by delaying the SpectrumSource by (NbrPartials in the spectrum source - DesiredTrackNbr + 1). For your example with 32 partials, if you set the Delay to 32 samp, the DelayScale would be:
(32 - !Track + 1) / 32.0
where the range of !Track is (1,32) with a grid of 1. (Of course you have to delay both the amplitudes and the frequencies, so the left and right channel outputs of the SpectrumSource).