获取VSTO中的Excel工作簿的Hashcode，以便根据状态启用按钮

I am creating a VSTO Ribbon AddIn for excel, and I am storing some workbook state information in my application that I use to update visual Buttons Enabled. Considering there can be multiple workbooks I am storing this state object in a dictionary in the ThisAddIn class. My problem is that I don't know how to get a unique Hash/Key/Guid for the workbook because all I get is a COM wrapper that continually changes the hash. fair enough, I totally understand that.I am creating a VSTO Ribbon AddIn for excel, an