Training a Dog to Use a Pee Pad?

How can I train my dog to use a pee pee pad when I get home late from work? I have a 6 yr old Shih tzu that is trained to go outside. My son has recently gone off to college so he's no longer home to take out the dog at a reasonable hour. I leave home early in the morning and don't get back till very late and don't want the dog to have to hold it until I arrive home. I was thinking of training him to use a pee pee pad in the house for those days he really has to go and I'm not home to take him out. How can I do this? Any suggestions?

By Lizette