Hooking Mixins and unnamed frames

[MuffinManKen]

I'm trying to hook WorldMapBountyBoardMixin:ShowBountyTooltip. There was a thread a little while back (http://www.wowinterface.com/forums/s...ad.php?t=56578) that I used for reference and what I took from it is that if I hook the mixin AFTER the mixin is created but BEFORE it's used on a frame, the hook will work. Looking at the WorldMap code I didn't believe this was the case, but I tested it anyway with this:

hooksecurefunc(WorldMapBountyBoardMixin, "ShowBountyTooltip", function(self,bountyIndex)
    print("WorldMapBountyBoardMixin:ShowBountyTooltip " .. tostring(bountyIndex))
end)

The print did not fire. The other method mentioned in that thread is to hook the frame itself, but in this case the frames are unnamed (just a hex string) so I don't believe I can do that directly.

So in a case like this, what is a reliable way to hook the method?