Hello Samuel Jobin,
Sorry for just getting to this but I see this as a unanswered post from December and wanted to reply.
In your post, you mention that solution 1 (table calc as a filter) and 2 - using duplicate data sources, are impractical. I'm very curious why this is. The duplicate data source one contains another connection to the data source but does not imply duplicating the space of the data source. Is it impractical because of the size of the data? In addition, what about the table calculation solution does not work? Usually, filtering a view with a function such as Lookup() works quite well to show only a current month while maintaining the values in the view to do percent of year or percent of total calculations.
A bit more detail about the first two issues might lead to a potential solution. As for RAWSQL functions, they are applied without filters to arrive at the data passed back to Tableau.