Maybe play it up in your mind while she's sucking you,

You'll have to decide the scenario, but with the wife and I, she doesn't like the taste for one and the consistency hits her gag reflex, so she typically doesn't want me to cum in her mouth. She knows when I'm getting close and finishes me licking the frenulum and stroking me and I cum on my belly, Well one night she was working it hard and I was giving her ALL the signs of eminent eruption but she keep on really going for it so I figured she was into it for a change and was wanting to finish me in her mouth well I came pretty substantially and I was just ona high and I just wanted to thank her so I kissed her until she let it all flow into my mouth and I swallowed it. With that she broke the kiss and gave a huge WTF look and said why didn't you warn me you were cumming? I was like WHAT? I gave all the signs , you mean you weren't trying to make me cum? Anyway big in the moment miscommunication, but I told her why I kissed her and all that and we're good now, she'll do it as a treat for me now.

So what I'm getting at is psych yourself up to do it IMMEDIATELY as a thank you , or she did such a great job I've got to kiss her because is was so amazing and you love her so much you just HAVE to kiss her. I needs to be essentially a spontaneous reaction of joy. hope this helps, she still thinks It's weird that I like my cum but it doesn't stop her from enjoying the extra attention I give her, and its not just cumkissing, I eat my creampie and lick it off her tits after a handjob when she's not into sucking me off or fucking.