Prison Server Ranks and Donator Ranks

So I'm working on my prison server and I ran into an issue. So if you know anything about prison servers there is the ranks A-Z. If I were to keep my server with only those ranks then I would be fine but my problem is that I'm trying to add Donator ranks and I couldn't find anywhere about combing 2 ranks, for example, someone who is in rank F and they donate for a rank called VIP, how can I make it so that they have the permissions from rank F and also from VIP. Hopefully I am making sense if not post a reply. Thanks

Permissions Plugin - PermissionEX
Rankup Plugin - Rankup​

 

What you need to do is add the group onto that user so they are in more than one group by the command /pex user <player> group add <rank>
But i uncovered a problem with the ranking up plugins and what they do is set the user to the rankup group.
So to get around this I us http://dev.bukkit.org/bukkit-plugins/serversigns/ and set the rankup command on there with a price.
Any more help or questions ask.