How can I keep this feeling going?

I am a long time Aneros user, first using an MGX for about two years, and more recently a Eupho. I plan on buying myself another model soon. But what I wanted to post about is a feeling I get when I use the Eupho that I really enjoy, but can't seem to make last. When I use a Eupho. a few minutes after insertion, shortly after the involuntaries start, I get the sensation like the Eupho is hitting the internal end of my penis, that is the end inside my body opposite the head and I feel the stimulation going right up the shaft. It almost feels as if I could prolong this, I would have a hands free ejaculation. I should tell you that for me, the best position is a kneeling one, and my favorite technique is the do nothing approach. Usually when I am having my most intense sessions, I almost never have an erection, only a chub at best. But this particular sensation almost feels as if I will get a ragingly hard erection, but it never lasts more than a few waves, and then I go onto other things. Now mind you, I am not complaining about where I go from there, and my general experience has been that letting my body do whatever it wants to do has always been the most effective approach to my aneros experiences, but I was wondering if anyone had any suggestions.