I was not aware that alcohol or solvents would harm an O2 sensor. If this is indeed true, I would suggest using a propane torch to burn the carbon off. The sensor is resistant to high temperatures by the nature of the function it performs and where it is located, so as long as you don't get it hot enough to melt the wires, you should be OK. If you don't like this idea, perhaps scraping the worst of the deposits off of the outer protective cover (the slotted part that goes inside the manifold or cat) and installing it, and letting the heat of normal operation burn it clean would be the best thing to do.