It is impossible to embed any JavaScript- or Flash-based widgets (essentially anything more than text or basic images) using WordPress.com widgets due to security issues this functionality introduces (it becomes extremely easy to redirect visitors elsewhere, including to malicious sites). This is the same reason why WordPress.com users need to use the static 20SB bubble badges instead of the Flash-based widget.
Unfortunately, if you want to use JavaScript- and Flash-based widgets, you'll need to move your blog to another provider or host it yourself.