How to make him cum inside easier?

Hi everyone,

We have been trying to have a baby, but the problem is that he can’t cum inside. For him it doesn’t feel the same, as he is so used to making it with a hand job or blow job. He has an excellent erection all the time. We can have sex for hours, but when it comes for him to cum, he still can’t cum inside naturally. Please help. Any recommendations? Thank you.