I have inserted some code manually to get the G+ button with Share & Follow.
To elaborate: the HTML-code is based on the code that is outputted by the Share & Follow plugin for other buttons, so if you use buttons of another size, the code may not be fit for you. Feel free to change it to fit your needs, because it’s quite easy.
I entered this code between line 379 and line 380 of saf-functions.php:
$html.="<li class=\"iconOnly\">
<a rel=\"nofollow\" target=\"_blank\" href=\"https://plusone.google.com/_/+1/confirm?hl=en&url=$page_link\" title=\"+1 this post : $page_title\">
<img src=\"https://blog.mydomain.tld/wp-content/plugins/share-and-follow/images/blank.gif\" height=\"32\" style=\"background: transparent url(https://blog.mydomain.tld/wp-content/plugins/share-and-follow/images/google_plus_32.png) no-repeat;padding:0;margin:0;height:32px;width:32px;\" class=\"image-32\" width=\"32\" alt=\"google+\">
<span class=\"head\">+1 this post</span>
</a>
</li>";
The image used, I saved it myself, but can easily be found on google image search using this query string: “google plus 32”