GroupManager Subgroups (help)

Hello to anyone that reads this, I was wondering if you could help me. I am group manager stupid and do not know how to create subgroups. What I mean is I have donor ranks on my server for example I have my platinum rank. I also have a prison minigame on my server. What I want to be able to do is for my donors or Platinum to be able to play the game. So for example when they buy the rank and they first play prison, I would like their name to be [A] [Platinum] {Name}>> {message}. But I do not want to manually add each Platinum perm to them and just give them an extra prefix, so I was wondering if any of you would know how to help me, thanks in advance.

bump

EDIT by Moderator: merged posts, please use the edit button instead of double posting.

 

Sub-groups are just a seperate group you add to user.
Take a look @ this page.
http://wiki.ess3.net/wiki/Group_Manager/Commands