Lady was outdoor trained for years until I was in a car accident and couldn't take her out while I was recovering. Now I am a pee pad convert and would never outdoor train again.
I put the pads near the back door where Lady scratched to go out. I have one of those really light Seabreeze pens that I circled the pads with after meals, nap, or when she asked to go out. She was frantic at first, scratching the door and she couldn't understand why I wouldn't take her out. She couldn't hold it forever, though, and as soon as she went I did the happy dance and gave her a treat.
I also blotted up a bit of urine from the wet pad with the new pad to "scent" it for her.
It only took her a couple of days to figure out that this was a pretty easy way to get treats!
Of course, years later she still expects a treat. She will sit on the pad (or lie down if I take too long) and bark until I give her her Itty Bitty Buddy Biscuit. If I don't take the pad up right away, she'll go back to it and try to get another treat out of me!
There are so many advantages to having a toy breed dog pad trained.