It is a little bit tricky having to generate the unique "option custom-if-n-m code ..." lines at first where n = pool index and m = item index in the items of the pool. Then make sure to reference that later, getting the same pool index into the array of pools. The $all_pools array as the "overall" or "base" pool first (at index 0), followed by the user-specified pools at index 1, 2, 3,... - which are actually at indexes 0, 1, 2,... in the ordinary array of pools in the config. So the -1 at line 910 has to happen.
But it works for me.