If you really need to auto-post material to your site, perhaps you should set up a self-hosted site instead.

You could probably add a twitter widget to your sidebar for usernameX. That's not a problem or you could set up an RSS widget for your sidebar if you have the feed to that username or topic. If you do it would be great to share how you did it because twitter pretty much did away with that option with their redesign.

Is there a way to make the Twitter Blackbird Pie widget (http://en.support.wordpress.com/twitter-blackbird-pie/) automatically read from a Twitter feed/list/username and post tweets to my blog as posts?

We can use the Twitter widget offered by WordPress.com, which you can read more about here, and which also explains other ways to integrate Twitter with your site. http://en.support.wordpress.com/twitter/

<script charset="utf-8" src="http://widgets.twimg.com/j/2/widget.js"></script>
<script>
new TWTR.Widget({
version: 2,
type: 'list',
rpp: 30,
interval: 30000,
title: 'title',
subject: 'subject',
width: 'auto',
height: 300,
theme: {
shell: {
background: '#ffffff',
color: '#ffffff'
},
tweets: {
background: '#ffffff',
color: '#000000',
links: '#755e4f'
}
},
features: {
scrollbar: true,
loop: false,
live: true,
behavior: 'all'
}
}).render().setList('username', 'listname').start();
</script>

How can I embed it in a WordPress.com Page please?

Thanks