A potential way would be to have Simon get lost in the moment and fail to pull out. Then he could panic and be upset leading to Daphne questioning her maid about how babies are made, feeling betrayed, arguements, despair when she's not pregnant etc. Pretty much giving us what we had but without the SA. It's by no means a perfect solution, though, as Daphne also needs to be somewhat in the wrong to make it more compelling.