Physical Inventory and Lot Numbers

Our client has V4.00 SP2. They use lot numbered items.

They generate a physical inventory journal by location. There are 2 lot numbers for one item at location X. The counted quantities differ on the lot numbers and on the item overall, as follows

Lot     Calc. Phys.  Difference
ABC     10     100     90
DEF     30      20    -10
 
Overall 40     120     80

So the overall journal line is a positive adjustment but one of the lot numbers needs to be adjusted down (negatively). You cant enter a negative quantity in the item tracking lines. How is the client supposed to enter this into the journal ?

In fact I will be dataporting the counted quantities in from a spreadsheet, but the principle is the same.