Potty training when you can't control all the variables

It seems like the parenting zeitgeist is all about potty training lately. I got three questions on the same day about potty training last week, and have been thinking about it a lot myself lately because my son will be three in May and isn't out of diapers. Then yesterday I spent the afternoon with my BFF and her husband and son, who is almost three and still not completely potty-trained.

As long-time readers know, my older son pretty much potty-trained himself. He started wanting to try it at 16 months and was just really into all things potty. He'd be our bathroom attendant and hand us the toilet paper, stop to observe dogs pooping and peeing on the street, and watch the Bear in the Big Blue House "Potty Time" DVD on a continuous loop. He was in underpants by 27 months during the day, and by 32 months at night.

So I've got nothing, because I didn't really do much of anything other than go with his interests.

The younger one is more of a challenge, though. His personality is completely different, and he really isn't convinced there are any benefits to being in underpants. Plus I'm at work all day now, so I don't have the same ability to control the situation on a micro level. And it's harder to just leave him in underpants all day and not worry about accidents, since we have to leave the house more to work around his older brother's school schedule.

We've talked here about potty training several times in the past few years, and as usual you guys have been a font of information and experience. I'd like to open up another discussion about it, but pick your brains for ideas about training a non-only child who is at the whim of an older child's schedule, and also for training a child (who isn't so sure about it) when there's a childcare issue involved.

Help?