[EagleNick]

Hm, they could have used a conditional around the rank code in the postbit template so that the rank image for Premium Members is clickable.
Like this:

<if condition="$post['rank']">
     <if condition="$post['usergroupid'] == X">
          <div class="smallfont">
          <a href="payments.php">$post[rank]</a>
          </div>
     </if>
</if>

The code in blue is what you should add. Change the X to the ID of the Premium Member group.

I just posted this off the top of my head, so try it out and let me know if it doesn't work properly. I didn't test it.