As of right now, I don't think there is a way to make Prime Brothers Chapter specific. In theory, I guess you could try giving them Counter-Attack for the corresponding points for each unit from the Wolf Brothers detachment sheet.
Seems like it would be an interesting update for the Prime Brothers, just a table of Detachment abilities with points costs, and you have to pick one to apply to every unit in the force.
Hmmm I see what you mean... at this point I'm a little torn. Either I will have to either modify the detachment upgrades as to include the Prime Brothers, or else I will have to integrate them into the standard Battle Brothers list... not sure what I'll do but something will definitely change.