You mention that you have issues over the taste. Do you also have issues over the texture or over the actual ejaculation sensation eg it is warm or there is a squirt sensation? Thinking about that is important in respect of what is 'doable' or not.
If it primarily a question of the actual taste then I will make one other objective observation. You say you have done it once and you definitely did not like it. I get that. However, there are two reactions we can all take to unfamiliar tastes. We can either become accustomed to them through repetition or we continue to instinctively 'distaste' and there is no simple solution. For example, and you may feel this is not an a valid comparison, but on first taste I disliked the taste of garlic but over time I became so conditioned to the taste I now love it. On the other hand, I periodically retry eating blue-veined cheeses and no matter what just can't accommodate the taste.
If you really feel that you cannot overcome your dislike for the flavour I can only suggest confectionery. Chewing gum? Either mint or cinnamon? Or hard-boiled sweets? Again, either mints, mild or sharper depending on what he can tolerate. Or else fruit or spice-flavoured ones, eg cinnamon or clove? What about Tic-tacs (US equiv?), progressing to larger sweets, eg humbugs, over time the hardness of which you can use as part of the fun, pressing it against or rolling it around his head?
One last aside, which is not directly related to your post but I think still has relevance. Does he know what the taste of his own semen is like? I think, given the context, he should. In fact, all men should know what the taste of their own spunk is like, if they expect or even hope that their partner will permit them to orgasm in their mouths. And it is definitely NOT a gay thing.
Oh, one last thing. Some experts (?) attend that swallowing sperm is beneficial for women, not only health-wise but also because within semen there are hormones and proteins that actually psycho-chemically enhance the bonding process with your partner. I am somewhat dubious about that, being the cynic that I am, but Google it for yourself and make up your own mind. Even if it is only psychological well-wishing, how much harm can there be in that?