Ha ha, yes, I just meant that it's a problem you don't need to have. When I have smallish boxes like that on a responsive design, I just leave the boxes at one size and let them drop when needed, or just become full width when the screen gets very narrow. Much easier.
I'm not up to speed with the best CSS3 solution, but this will also introduce the problem that some major browsers won't support it, so you'll be stuck with that dilemma too.
Anyhow, I'll get out of the way and leave space for the CSS3 experts. I was just trying to save you some hassles by offering another perspective.