When I first started playing D&D, I wanted to do all kinds of crazy stuff, but people were like, "Wow...that's out of left field...we're going to rescue the princess" So, I started making characters who are more organized, more lawful, more inclined to just "go with the flow".
Then, in my new game group, suddenly the DM was asking me "So, what does your character like to do? Why are you an adventurer?" I was floored...
After that, he would work with each character a little bit individually to have something that's happening to just them...it doesn't totally take your character away from the campaign, but it's something that's developing on the side, and you can include or exclude the other PCs as you will.
End result, I'm more "go get 'em" with my characters now, and my DM is totally willing to work with that.
I'd suggest this: Talk with each person a little bit seperately. They might have something in mind, or a personality trait that could be fleshed out into something on the side, but they might be sort of hesitant to take the reins. When my DM was doing sidebar stuff with me, I almost thought I was taking away from everyone else's fun by having only me playing for a while...but, it works out.
It's like the Star Wars movies...the hero's aren't always nessecarily in the exact same place, or doing the exact same things. They might all be working towards the ultimate goal of overthrowing the evil Emporer, but they might have different methods.