Note: Some words are not showed to me in English, so I will try to suppose how that words figure out.
1) Write a new PAGE (not Post)
2) Paste on the title (subject) the exact code that you get from Google Webmaster Tools option “Upload an HTML file” (this is the verification method you have to choose). Example of the code:
3) Click to publish it.
4) Ask Google to verify your Blog.
Just that! It worked for me.
UPDATE: “wordpress.com does have a place where all the major search engines can verify your site. just go into your admin and go to tools and at the bottom is Webmaster Tools Verification” (Thanks to Daforuiner).