This is a tricky one, I'm not sure quite what you're looking for exists without modification. A hollow strap-on might have some structural issues.

The Love Booster might meet part of your needs, but being made of silicone, it might lack the needed rigidity, it's more of a penis extension with a support harness than a traditional strap-on.

There's also the Miss Boss, which has a small sex machine built into it, but it covers the crotch. And I think the crotch plate is load-bearing. Might be an option if you feel up to re-engineering the whole thing, but it would be an expensive method.

This could require a modified or custom-made harness, if you remove the bottom part of the crotch plate, the base the dildo mounts into is more likely to flop around. You might have some luck adding thigh straps to something like the Beginner Pegging Set, or you might be able to add a pair of straps that go around the penis and still link up to the lower strap, but that may be uncomfortable.

Everything I've mentioned is available here on EF, might be worth having a look around the strap-ons available even if modification is needed.

I hope this helps. less

I know this post is a bit older, but if you still don't have something that has worked well, my first thought was something like a quality cock ring with a sturdy double penetrator attachment, Like this one. It might also require a modification or being flipped around, or secured with a harness for more rigid support, but it may work as is. It's made for anal play but I see no reason why, if it was done in the right position, it couldn't work? You might shop around a bit and see what kind of similar items are out there, but the one I linked is the most similar one Eden has to what I was thinking!He can also work on reducing his refractory period through good physical health, particularly cardiovascular health and exercise, but it's not a guarantee and there's no formula to know how much it might help. If he's already in top shape, then unfortunately it would be a matter of medications to try, but I wouldn't go there if he doesn't have trouble with erections in general. I feel very lucky, my ex-husband had a long refractory period but my current partner has virtually none. It takes all of a minute or two before he's good to go again. I honestly was shocked that was even possible, but it's a blessing for us!I wish you the best of luck in your quest! less