Projecting Forecasted Business over Future Months

I am looking for a creative solution for a business reporting situation. I am working with a customer that wants to see their annual volumes from sales distributed evenly across those 12 months. For example, they are forecasting a sale in March that is expected to start producing volume (let's say 12,000 lbs.) on May 1. They want to then evenly spread that volume across the next 12 months. That prospect/sale will be combined with all other business, so they can visualize their monthly volume on a dashboard (maybe delineated by forecasted and confirmed sales).

I can't think of how to achieve this and was hoping that someone out there may have solved something similar in the past.