We have tried this a couple of times. We decided it was better to take it in small steps and leave them free to roam while we did quick errands (about 1 hr) and then bump it up to a few hours while we were at the hockey games. We are currently trying to get 5+ hours but are not having good luck. They do well for a few days even a week or so and then seem to have the "I'm mad at you for leaving me" poop, lol.
I've never tried the pee-pad though as they never sem to pee inside. But using it would give me the same fear that they would think its ok to pee inside.