Not Swallowing It Either
You recently published a letter from a guy who had been told his cum tasted bad. He wanted to know how to improve the taste. One way to have your man "get it" is to spit the cum back into his mouth and let him taste it. If he's not willing to do it, that should be the end of that argument.
I'm glad you mentioned checking with your partner to make sure he is willing to try this, before just spitting a load into his mouth. The shock of such an unexpected experience could prejudice him against the whole point of the experiment—for him to get a sense of what he is asking his partner to do. I would take this in a slightly different direction and ask him to just taste his own ejaculate the next time he masturbates. If he thinks it's untasty, it seems unfair as well as unkind of ask a partner to ignore that fact.
I want to add a couple of other things. One is that I heard from several self-described cocksuckers (men and women) who pointed out that if you have a cock fairly deep in your throat when the man ejaculates, the cum is going to bypass your taste buds anyway, and you'll have little problem with the taste.
I also heard from one woman who kept a bunch of tissues in her hand during oral sex. She discreetly spat the cum out afterward and pretended she was blowing her nose. That way, she spared both her tongue and her partner's feelings.
One man who wrote to me said that he would prefer that his partner simply refuse oral sex, if she didn't want to swallow the ejaculate. "There are plenty of other things we can do," he wrote. "And I would prefer to avoid getting the impression that she finds my sex disgusting."
Finally, I was remiss in not pointing out that there are some sexually-transmitted infections that can make ejaculate taste funky. I should have suggested that the guy who wrote to me get tested for the usual complement of ailments, just to make sure he was wielding his wiener with a clean bill of health.