I recently went through this with my new addition who was outdoor trained and I wanted him to be able to use pads.
He took to peeing on the pad fairly quickly, but for poop, I had to force him. I gauged when he needed to go and then confined him to the back kitchen hallway with 6 pads lined up. Spent the next 20 minutes telling him that it was okay to poop on the pad. Finally, he did it, and I praised him, did the happy dance, and gave him a treat. I showed him how I clean it up immediately and bring it outside -- both my boys love this little ritual.
My Teddy is a bit of a dancer, so it took a couple more days for him to learn where to place his back end on a single pad.
When he gets it right (which is 100% now), I throw a party -- which he loves.
Both my guys prefer a fresh pad to do their "big" business. Hope some of this might help you.
Good luck!