It crossed my mind but It sounded a bit « dirty ». Is it good practice ? I can’t think of any obvious reason why not after all...

I have seen quite a few solutions using this method to power-up low power circuitry. The power-off current is reduced to zero by toggling the I/O. The I/O supply can be quite noisy though. I think it will work without problem in your application.

 

I have seen quite a few solutions using this method to power-up low power circuitry. The power-off current is reduced to zero by toggling the I/O. The I/O supply can be quite noisy though. I think it will work without problem in your application.

Would a simple ferrite do ? How about a couple of capacitors connect to gnd ?

 

The simplest and easiest solution would be to take a higher number of ADC readings and average the value.
A high capacitive loading would not be good for the I/O and is usually limited to a few tens of pF (see datasheet).