You can do that, but it will still only be possible to do the isolation with very small value capacitors, so the current into the load is under the threshold of causing damage. thus if your circuit can operate on under 500uA maximum, and is fine with much less, then you can make an isolated supply using class Y capacitors as isolation.
Not sure on the exact value for current, but it is pretty low to allow you to have the double isolated rating and still have class Y capacitors in there, and typical capacitor values are under 1nF in most cases for that between line and earth and neutral and earth.