Adding a custom field to Storage Summary screen (too complicated?)

The customer asked me to add the Qty Avail to the Storage Summary inquiry grid.  Seems simple enough.  I pulled the value from the INLocationStatus table.  However, that value doesn’t necessarily match the Qty Avail in the Inventory Allocation Details screen (“IAD”).  On the IAD screen, it takes into account Plan additions and Plan Deductions to get the Qty Avail value.  The IAD screen has a relatively HUGE set of filters and BQL selects to get the value shown on that screen. 

I looked at the InventoryAllocDetEnq graph where Qty Avail is calculated for IAD.  It is very complicated.

Since I would have to do that big set of selects/filters/calculations for EACH line selected on the Storage Summary screen, it will definitely have a big performance hit as the Storage Summary screen can return thousands of records as this customer has many thousands of inventory items.

I used the RowSelected event to pull the QtyAvail from INLocationStatus as it is a simple select from one table.  Surprisingly, it does not impact performance of that screen is a significant way.  However, if I had to duplicate the work done on IAD, it would for sure be a problem.

My other thought was to create an instance of the IAD graph, plug in the filter values and return the value from the field on that screen.  But that seems like it would also kill the performance of the Storage Summary screen.

Would it be safe to say to the customer that this just isn’t doable?  I mean, I “could” do it, but it would kill the Storage Summary screen.