I do not know of a way to achieve this with Macola or WMS "out of the box". It can be done with an enhamcement. If you are using WMS and packing pallets you should be able to determine the number of pallets and add 55 Lbs per pallet to the weight. If you are not using WMS, you would have to either provide a screen for the number of pallets to be entered or enter a Pallet Item to record the number of pallets.
The ultimate solution depends on your shipping process.
I thought Exact was thinking about adding this capabilty to WMS, are you on the most current WMS version?
Nick