PBA,
Yes.
However, I don’t know if the right word is “therapy.” I think that if I devoted myself to becoming gay, I probably could do it (and if I would fail it would not be because it was impossible but because it was too difficult and I gave up).
I think that part of the perception that it cannot be done comes from people underestimating the plasticity of the brain and the power of the mind. If people can suppress the need for sustenance such that they can go on hunger strikes for months despite food being put in front of them, then people can suppress their sexuality as well.