Well yeah we don't have the pelvis for it. If someone tried shoving something the size of a baby through our smaller, fixed pelvis, it would shatter and likely lacerate arteries in the process. We definitely could not handle it. There is no surgery that can make this guy capable, you're absolutely right. For so many reasons it's just not possible.
BUT, having followed these insane people for a long time to learn exactly their level of delusion and beliefs, I know what he really means to say. He means that he can mimic a pregnancy and it will be "real", the same way they've been mimicking periods and claiming they're real. What he'll do is get a female partner (which by his definition can also mean a trans woman aka man). They'll decide to have a baby, and he'll become the "pregnant" one. What this means is they'll either adopt a baby or go the route of surrogacy. Probably surrogacy. He'll wear an appropriately sized pregnancy suit throughout the 9 months, mimicking being actually pregnant, and go to all the birthing classes and such for "affirmation."
Yes, they really do this, and this is absolutely what he really means.