There are several ways of introducing a partner to the idea of you being denied or both locked & denied. There are of course some slightly deceitful things you can do as well. Some ways are better than others in that they work and some don't work so well.
My immediate thought is that one should never advocate any dishonesty in a relationship but sometimes the end may be considered to justify the means. And to be frank a certain amount of being less than honest has been helping keep the cart on the rails for years.
Your 20 minutes late setting off and she has just tried on her 4th outfit, Does my bum look big in this? What are you going say? ..NO. I doubt it.
You were late because you were watching something on TV ... sorry the traffic was crazy today for some reason.
Nobody got hurt but dishonest all the same.
There is lots of published material on male chastity and how to get started and perhaps tailoring one or a combination of some of those might provide a possible solution for you. Ideally this is probably the best approach.
If your partner is not that open to ideas that are other than vanilla perhaps introducing the idea of you not having an orgasm every time you make love. She will want to know why, even if she does not ask. Tell her you are getting enhanced feelings aout of feeling honry for longer. You, ought to, know your partner and what she might consider believable. Then its time to show her the benefits of that.
She gets more attention when you have not cum. Not just in bed ..all the time in every way possible. Do things for her so she is less likely to be tired. Do stuff you don't normally do and do the stuff she normally has to ask you to do before she asks. Ring or text her during the day, and not just about sex. Basically start courting her again. You know what worked back then. Then the slight dishonesty... allow yourself to be a little less attentive and do a little less after you have cum. Then pick things back up slowly till normal service is resumed. She will notice. She will ask. Which might be your cue to suggest looking at some of the stuff you have read, or it could be time for a little more dishonesty ..Sorry I don't what makes me behave that way... let her figure out that things are better before you cum than they are straight after.
If the end result is you being denied and perhaps locked too then you will have attained what you want, the dishonesty this may have required to achieve it is onlyreally justifiable if you are prepared to really work at making it worth her while in everyway on all levels and on a permanent basis. As she realises the advantages to her she is far more likely to embrace the whole idea and then it won't be long before you are enjoying regretting ever starting this.
Whichever way you go ...good luck.