Cost Forecast

We have the scenario as follows:

We do not have activity-assigned networks & we have only WBS elements hierarchy up to level 3. Hence in our case the forecast consists of actual costs through the period closed and expected costs for the subsequent periods and years. The actual costs are obtained from standard reports. The forecast costs are developed from prior period forecasts/historical data or it is developed from scratch. These forecast costs that are downloaded are manipulated in Excel spread sheet. The forecast are maintained in Excel spreadsheets (Tab De-limited File) & then uploaded into SAP through t-code CJR2.

The users are not comfortable with download and upload method of forecasted cost and wish to know alternate method. Even users are ready to manually update of forecast in project. Is that possible?