Ouch! That is some problem.
Like you probably already know from my other posts, discovering DL play worked very easily for us - none of the challenging psychology that you describe.
I'd try wearing and wetting under your normal clothes once in awhile - not to be "in his face", or in the expectation that it will immediately turn him on, but because it turns you on he may catch on that this is a good thing. Let him know that you have a puffy butt, but drop it there - it is your interest, does not have to be his too. Can't think of any other "gentle" way.
My honest, but unhelpful, viewpoint is: kink is only long term fun when it works for both parties. My wife and I are into a wide range of alternative activities. They are fun because we both enjoy them and find them very erotic. My online DL couple friends report the same thing - the reason it is so much fun is that both people are turned on by it. It would not be sexy if one party was "acting".
And yes, look for something that turns you both on. Find out what menu items turn him on, if you're lucky, some will work for you too, big time. But if he is as un-enthused about DL games as it sounds, I'd not expect him to suddenly "convert".