I've tried walnut oil, but I have to say, I went back to olive oil because the Walnut oil tasted like machine oil to me, whereas olive oil, though excessively oily as all the rest, at least has a slightly sweet aftertaste. I did switch to extra light o. oil, which seems to have the least taste of all.
Here's the way I cope. I mix up my mixture, stick a straw in it, plug my nose and chug it down. Still holding my nose, I go and brush my teeth, rinse my mouth thoroughly and THEN let go of my nose. This works great. You don't taste the oil at all unless you burp. (Pardon me for being gross, but on this forum, as you've probably noticed, burping is pretty polite for what else we have to discuss!)