You can also link to the Admin Panel from the default splash screen. @ my work everybody uses a link to FOP2 and only Admins ever go to the root splash screen, so this makes sense.
In that case, just make it /var/www/html/fop2/admin/ NOTE THE TRAILING SLASHS!/
For Older FreePBX (Like Version 2.9ish) read here.
Note this doesn't actually integrate with FreePBX management, I'm looking into that, for now this just redirects the buttons for User Panel to FOP2.