I recently needed to add this to the list of sharing links on a website. Seems the code is JavaScript and as such not possible to add to Sharedaddy without a little help. I’ve tarted up the code and put it into a tiny plugin as it may be useful to someone else. The plugin requires JavaScript but since +1 won’t work without JS I don’t think it’s a problem. I haven’t bothered to try and add it to the WordPress official plugin site because I’m hoping that in the next release of Jetpack they’ll add Google +1 and render this fix obsolete.

You can find FRP Google +1 For Jetpack Sharedaddy WordPress Plugin here.