First move everything on the disk to the end with "jkdefrag -a 6 c:", and then move the folder with the game to the begin of the disk with "jkdefrag c:/games/thegame/*".
I've just done similar. What I did was:
-a 6 to move all files to end of disk
-a 7 ONLY on the game directory
Then -a 7 excluding
the game directory (Though you could just run a standard -a 3 defrag at this step for speed with exclusion of game directory)
This puts the game files at the start of the disk in alphabetical order followed by the rest of the disk data. Assuming the game data rarely changes you could continue running JKD in future just excluding the game directory, it will then stay at the front unchanged (whereas if you didn't exclude it, it would be moved again)