I contacted HP about this problem, that it was not possible to have alternate "From:" addresses in HPOV SD. Although the field "From:" was available to use in rules, the alternate e-mail address was not assigned. HP "solved" this in SP24 in their usual manner, by making the "From:" field unavailable in rules.
Just thinking outside the square, isn't it possible to use an email address that is shared in Outlook. So all the admins will access this single shared email address and only look at their own region's email.