Confidential Data with Data Gateway

Hi, 

Currently my company is looking to set up a datagateway to avoid us having to do lots of manual refresh of reports. The report pulls from a few different excel spreadsheets, one of which contains information we do not want customers to see. If we set up a data gateway is there any way that customers can see other tables in an excel file that are not part of the Power BI report? I have looked at the analyse in excel feature and a few other things and have not found a way to do it but we need to be certain they can not before we impliment the data gateway. 

Just to be clear, this is the set up we have in the excel spreadsheet: 

Table A - included in power bi - table names and columns visable with analyse in excel and the online reporting 

Table B - contains confidential information we can not share with customers - not imported into Power BI at any stage. 

Ideally, we would remove Table B from the spreadsheet but unfortuantley we need that data to calculate Table A. 

If anyone could help me out it would be much appreciated!