I have a piece of code in the postbit legacy template for all users that havent verified their account for use of cirtain forums. Perhaps you could use this?
HTML Code:
<if condition="$post['field35']"><div class="smallfont"><div class="highlight">Member Status: $post[field35]</div></div></if>
Field 35 is text field called "Account Status" and in it says "unverified". when a user verifies there acount it will be removed.
Im sure it could be played with to do what you want, like:
HTML Code:
<if condition="$post['usergroupid'] == xx"><div class="smallfont"><center>Account requires e-mail activation</center></div></if>
You would need to put this in the right place on your postbit or postbit legacy template, and al you need to do is replace xx with the usergroup number that is for account not verified