Or practice by drinking ten pints and trying to run............ :o)
Seriously, the only way to get used to it is to practice it. I don't think you ever get rid of the feeling, you just get more confident about how quickly the feeling will wear off, so you can ride it out.
Also, try cycling the last half a mile of the bike leg in a gear that feels slightly too easy. The spinning motion will restore proper blood flow to your legs. (Easier said than done if there's someone up ahead you feel you might just catch!)