Here's basically the scenario.

All products of all categories have one price to follow. Say, $2.

Except for one product, the customized product. The category it belongs has no other product except it. And it's worth, say, $20.

Now my problem is, how do I set a typical global quantity discount (using that downloadable module or something else) to all products except that customized one?

I tried changing lines inside ot_qty_discount.php but I am still confused.

Will appreciate anything.