Two ways that I have used.
1. Set one of your staff to invisible mode then in your forumhome template find
Code:
<div>$activeusers</div>
Replace this with code mimicing the one below, placing the name and profile link of the invisible staff member in there.
This is taken directly from my site to give you the template to follow. Ensure that any username markup is also applied to each entry as appropriate.
Code:
<div>
<a href="http://www.peterska2.co.uk/member.php?u=54">Alice</a>, <a href="http://www.peterska2.co.uk/member.php?u=300">TechnoGeek</a>, <a href="http://www.peterska2.co.uk/member.php?u=235">Tom</a>, $activeusers</div>
2. Create a new mod/admin/whatever and repeat the above template changes.
If you want to know how it looks, take a look at
www.peterska2.co.uk
Tom, Alice, and TechnoGeek are my three bots so never show up logged in unless I make these changes.