Need to Exclude certain supplies for certain items from Pegging to Demand in Supply planning

Summary:

At present we are using Un-constrained supply planning. It's a global plan with about 4 manufacturing and 4 warehousing orgs. Manufactured goods are transferred from one warehouse to another, in addition to being transferred from the manufacturing org to its warehouse (for distribution). All of these movements are clearly defined in sourcing rules/assignments. BUT, there may be certain times when transfer orders are created ( directly in the execution system) that move certain items between 2 warehouses but business would like to exclude them from pegging to forecast/demand. (These are almost always not part of predefined sourcing network) .

These transfer order can be easily identified - (if item = 'IT1' and destination org = 'X' and source org = (A or B), do not Peg). I tried using attribute based planning, but could not figure out a way to use the condition as defined above. Plus, I would prefer not to have to use DFF when we already have the required attributes.