Bruce Lee has some exercises for just that thing. I don't know how effective they are, but I have practiced this way here and there. Also this way of practicing is most commonly done with the straight blast, you can use it for jab, cross. Never tried it with hooks myself, don't know if it would work for those.
Take the straight blast for example. Break it into four pieces. Halway out, full extension (impact), halfway back, and all the way back. Once you have this i mind. Throw the straight blast out as fast as you can, stopping halfway out, then continue to full extension as fast as your can, then full stop again for not even a second. Then pull it back to yourself as fast as you can, full stopping again for a brief second at the halfway point, then bring it the rest of the way back as fast as you can.
I know it sounds awkward. I personally haven't practiced this with enough regularly to notice any difference. But it did seem to work for bruce though. Give it a try, on your jab and cross. See if it helps. If it does let us all know. Feedback is always good
[This message has been edited by otobeawanker (edited 10-01-2004).]