If you use the "Notices" feature of 3.7 you could create a notice which has the sort links. (As long as you don't have too many prefixes you could do it manually).
Code:
<a href="forumdisplay.php?f=X&prefixid=Y">Prefix Z</a>
X - Forum ID
Y - Prefix ID
Z - Prefix Name
I remember seeing a modification that moves the sorting options above the thread list, you could maybe use that to enable people to sort better.