I seen this asked in the "Suggestions for your Site" I have done this on my site and thought I would share it with you.
Follow these easy steps:

Administration Panel

User Admin

Ranks
Now if you want to edit an existing rank, click on the rank. After the first rank add this <BR> then add the second title.
You have limited space so don't make the titles long.
Now to create a new Rank, click on add new Rank.
Now simply do as described above:
Title <BR> Second Title
And be sure to save!!
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