I have a 20 month old so I'm very interested in this as well. He always follows me into the bathroom, and I'm encouraging my husband to do the same as much as he's comfortable with that. I got a "practice" potty which he likes to sit on and play with (LOL), and I also got toilet "toppers" - they're toddler size seats that go right on top of the regular toilet so they sit on the "real" toilet but don't fall in. My son's over 3 feet tall already, so I figured it might be a good idea. I have to help him onto it, but heck, it's where I sit so I figure he might get it.
I'm wondering if showing him the empty toilet before you go, and the "different" toilet after might help him get the idea (kinda gross, I know, but goes with the territory I guess).
Thanks for asking the question :)