It looks like Wordpress.com doesn't allow any tags 'for security reasons'. Essentially, the Wordpress software can be obtained from Wordpress.ORG and installed on a separate website server and I believe that in that case the modification that you link to would work.
Here's what Wordpress.COM support said:
Here's where to get the Wordpress software:
Here are some ideas of good hosts:
A host costs a little money per year, but with it you could also buy your own website address and use your Wordpress blog as your site at that address without worrying about Wordpress.com making decisions for you. Unfortunately that would take a little work, copying your current blog entries over, etc.
If spending the money to get your own hosting is too much you might consider blogger.