iDataSort and desc only

I have 3 columns of data.

John 92 A+
Johnny 90 A+
Big John 89 A
John JR 65 C-
Little John 60 C-

The 2nd column must be hidden, and the 3rd column is sorted by the 2nd column, but I can't seem to find a way to make the sort desc only.

I'm looking for something like: { 'iDataSort': 1, [desc] }

I saw a plugin, but this approach seems like overkill given I have a numerical column by which the sort is happening. Also, a custom sort by the 3rd column doesn't work because the score covers a wide range of numbers.

Is there an easy way to do this that I've missed?