With ag_unitframes you can define your own groups. So you can create your own group "myBox" by specifying the names of your chars and you get your own custom group.
Agh! So close
Went and downloaded ag_unitframes r62957 from Curse and, just as you say, you can define your own raid groups, by playername. Very cool!

Unfortunately, a couple of issues...
I can't see a way to display player pets in a raid
It doesn't seem to support party targets, either

Thanks for the suggestion anyway, all I need is that feature transplanted into PitBull

For now, I'll stick with Pitbull and, in raids, will filter for Warlocks/Shammies only and ignore the other players.