You could actually do this yourself - if you open /includes/xml/ and observe the two ad_location_<>.xml files, you'll see how you can add custom ad locations. Add a new ad_location_<>.xml file and use the template from those two files.
You might need to do a bit of experimentation to find the correct X/Y/width/height variables to make it look good on the "Add New Ad" page.
Once this is done, you can go to ForumAds - Maintenance and click Repair Integration.
The last step would be to add the ad_location variable to the sidebar block you wish to include.