Shipping Oversized items?

UPS makes over-sized items jump up to something like 75 lbs even if it is only a 10 lb shipment.  We have a unique situation on a number of our items.

Lets say "Item X" is very bulk, but light at only 10 lbs.

Here is the problem.
We enter Item X into NetSuite like this...
Item X, weight = 10 Lbs.

BUT our supplier ships them in 1,2 or 3 unit boxes.  When they ship ONE, it is not over-sized and it does ship as 10 lbs and NetSuite calculates a fairly accurate shipping price.  When they ship TWO (which are always packed together in one box), the real weight is 20 lbs, but it must ship as 75 lbs because it is now in a "over-sized 1" box.  When they ship THREE (which are always packed together in one box), the real weight is 30lbs, but it still ships as 75 lbs because it is "over-sized 1".