It seems, this feature is not available so we have logged a New Feature request in our database to support it. We will look into it and implement it. Once, the feature is available or we have some other news for you, we will let you know asap.
This issue has been logged as
CELLSNET-45666 - Get SheetId field of Excel Worksheet
This is to inform you that we have fixed your issue CELLSNET-45666 now. We will soon provide the fix after performing QA and including other enhancements and fixes.
It is good to know that you were able to sort out your issue with newly added method. Let us know if you encounter any other issue, we will be glad to look into it and help you further.