Viewing and updating the forecast at Category level

Summary:

Our client wants to view and update the forecast in product category level in demand planning. The issue that I'm facing is each item has different primary UoM (each,Carton,Sheet, case etc).. Since this is a wholesale distribution industry 

there are multiple primary UoM for different item.

Now, when I view the data at Item-ORG level there is no issue since the forecast that I'm seeing is based on Item primary UoM. The issue comes when I view/edit the forecast at the Product Category level. Where each item under the Category 

has different UoM. We wont know the quantity is in which UoM at the Category level/Based on what UoM I will update the Forecast at the Category level.