使用sugar crm中的批量更新清除分配的用户

Our admin user has asked if it's possible to clear the assigned user of a accounts using the mass update functionality. At the moment, if he leaves this field blank the user is not cleared out from the affected records. But if I wanted to provide him with the "X" button to deliberately clear out the selection (as you get on the normal edit screen) I suppose I'd be looking at a code modification? Has anybody done something like this before and knows where I would need to make the change?Our admin user has asked if it's possible to cl