Forecast Comsumption for component item?

EBS R12.2.10 ASCP, MRP

Ideally: We would like to forecast at our subassembly item "SUB" and have the forecast comsumed by sales orders for the top level item "TOP" (both SUB & TOP are standard item with standard BOM)

Info: We manage production at the SUB item level as this item is universally used by many TOP items. SUBs have long lead times (5-18 months) but a TOP can be built within 3-4 weeks if we have SUBs in stock.

Issue: We are forecasting TOPs so the forecast gets consumed by the sales orders for TOPs. What we are doing now is: 1) forecast for TOP, 2) in MDS review TOPs and then enter manually into the MDS the build schedule for SUB in appropriate buckets (1 month of daily, 2 months weekly, 9 months monthly). In essence we use the MDS in a manner like a MPS.