Hi Tricia,
My suggestion would be to get him peeing on the pee pads while he is urinating outside...meaning, slip the pee pad under him while he is peeing then bring this already soiled pee pad inside for him to go on.
My thinking is if he smells an urine odor on the pee pad it might entice him to use it again.
Hope this helps.
Love and hugs,
Lori