Sorry about not being able to stay active here. I don't expect I could for some months to come due to the busy life here. But soon I'll be working or studying somewhere else. Hope I could have more time than.
By the way, Ive experienced doing Yoni Mudra Kumbhaka when holding back, just before the climax is reached if the stimulation is continued. To simplify the Yoni Mudra, usually I didn't press my eyes, and I used my thumb and index finger of my left hand to close the nostrils. (so my right hand is quite free) I don't do it every time I hold back. Just quite some time until the sensation becomes strong.
I've found that, while Tantric sex (TM for me...) can go on for hours without the feeling of being relieved, doing Yoni Mudra kumbhaka seems to have an effect of easing the desire to ejaculate. (after about 3-4 Yoni Mudra, with about 10-15 mins of normal stimulation-hold back in between)
Try on your own to see if it works. I'm interested to know whether it's useful in general for taming sexual desire, or I'm just a special case. I also wonder if doing Yoni Mudra this way can be more effective by combining the effects of tantric sex.