Yes I read this technique while I was searching for any answer to my question, but unfortunately there's 2 issues in this solution :
1. If you managed to show more than 1 sheet in the same dashboard you won't be able to let the user download from any of those 2 sheets beacuse in this technique Tableau will export only the first sheet on the dashboard alphabetically.
2. This technique will affect the performance of the dashboard if you have big amount of data in the underlying view, (which is my case) because Tableau will always generate this hidden view with all the underlying columns, and will take longer time to execute its queries.
anyway it is an interesting technique but won't suit all the cases, I'm sure there's more solutions we can find,