The opamps for the analog inputs and the ADC support a supply down to 3V, so I guess it should be possible if we can provide a regulated supply above 3V.
The issue is that the codec is powered from the PB2-provided 3v3 rail, which is on an LDO from the input voltage. So if your input is 3.2V, the 3v3 line will actually be something like 2.9V and more noisy, because the LDO won't be able to regulate properly. Things should still work - I believe - but you may have surprises.
