Here are 2 options for truly more stretchy bind-offs:
1. Knit the first 2 sts as you normally would. Pull the first over the 2nd, as you normally would. Now, take that 1 st you have on the right needle and move it back to the left. Now, knit that st as if it were new, and the next one. You now have 2 sts on your right needle. Pull the first over the 2nd, as normal. Then, take that 1 st you have on your right needle and put it back on the left. Continue in this way.
2. I don't like this one as much because it doesn't give you as neat an edge, but some people love it: For each stitch you knit, do a yarn over first, then pull the yarn over the stitch you actually knit, and treat that as one stitch. I know it sounds complicated, but it isn't. Just be sure to read the important note at the end about the YO's! It breaks down like this:
YO, K1, pull YO over the K1-- now you have 1 stitch on the right needle.
Repeat this. Now you have 2 sts on the right needle. Pull the 1st one over the 2nd, just as you normally do when you bind off. You'll now have 1 st on the right needle.
Repeat the first step, that is, YO, K1, pull YO over the K1, now you have the 2nd st on the right needle and pull the first one over it, as usual when binding off.
THE VERY IMPORTANT NOTE: When doing the yarn over, if it's right before a knit stitch, bring the yarn over the needle from back to front, which is the opposite of what you would normally do for a knit stitch. If the YO is right before a purl stitch, pull the yarn over the needle from front to back.