Let me preface this by saying that I am not as familiar with W/O as with other Module. W/O has not been fully updated to the Business Framework Standards so there are only a few object available that can be accessed through BOI.
The Cost Roll-Up Register does use an object and you should be able to process the update through BOI by instantiating WO_CostRollupRegister_Upd and calling the appropriate methods. At the very least, you will want to call the ProcessReport() method to process the report and then call the Update() method to update the register. There may be other method calls required.
Wo_CostRollupRegister_upd does not contain any public methods so there is no documentation for it in the Object Reference. However, it inherits from CI_CommonCostRollup_Upd and SY_Update which are documented in the Object Reference.
What version of MAS 90/200 are you using? The Object Reference for MAS 90 4.50 contains the documentation for CI_CommonCostRollup_Upd under Common information.
CI_CommonCostRollup_upd was not introduced until the 4.4 release, when Inventory, Purchase Order and Bill of Materials went to the 4.x framework, so it would not be available in prior versions.
