Reporting on Budget Units (BU) Planned versus Actual

We are running ECM on ECC 5.0. We are using Budget Units (object type BU) to track our budgeted amounts available for the different compensation plans. The problem is I cannot figure out how to report on the amount budgeted versus what has been spent.

Infotype 1520 (Original Budget) stores the budget ID and the amount allocated, but does not track any of the amounts that have been drawn from that budget as a result of compensation adjustments.

How can we setup a query to show the amount allocated from these budgets?