The link you posted above is to a workaround.
I've read quite a bit on the subject but it is never clear on what is possible as alot of documentation seems out of date and not applying to 3.x.
The documentation here > http://en.support.wordpress.com is continually updated. Moreoever, the upgraded version of wordpress are deployed here first at wordpress.COm and then are released to wordpress.ORG bloggers. So if you are reading anything on the internet it's probably for wordpress.ORG installs and not for free hosted wordpress.COM blogs.
The best way to get a clear answer about any specific widget is to post the code between code tags. Then Volunteers can examine it and tell you if it can or cannot be used and if there is or is not a workaround.