Use the regular login block?

you can normally add content to the end of a module generated code by using the hook_invoke_all(). This will allow to add formatted html to the end of the module generated content. The hook is documented on api.drupal.org but the general way of adding it to a module is to use your module name followed by the module name that is calling the hook (of course this could be wrong - it is from memory ;P

so, if your module name is yahoo_auth, you would add a function
function yahoo_auth_user($op) {
//your returned code here
}
You will need to check the parameters for this hook on the drupal api site or in the user module.

hth

oops, thought this was a forum topic, not a feature request. Ignore previous post.

Hey, no problem. Your post was very informative!

I'll still be looking forward to having one less block, though. Hopefully slimandslam will get to this at some point.

I actually have some sample login blocks that I created. None use this approach, however. I'll look into it. Good idea!