The Twitter devs vetoed that idea back in 2009 -- too much spam potential. Here's my 5-minute effort anyway:

http://www.wmorgan.net/lw_twitter.html

I don't have a Twitter account so the page isn't tested, but it looks like it works -- give it a second to load, though.

Edit: The following JavaScript will turn all Twitter links on this page into follow links. Couldn't figure out how to make a bookmarklet in markdown:

jQuery('a[href*="twitter.com"]')
  .addClass("twitter-follow-button");

jQuery(document.createElement("script"))
  .attr({"id": "twitter-wjs", "src": "//platform.twitter.com/widgets.js"})
  .appendTo("head");

There is, sort of. You can create a list of people, and then other people can follow that list as a group. If people are added to the list later, you'll end up following them as well.

So, you could create a global LW list and various local LW lists, if you wanted.