Report Filters - Dates prior to Current Month

I want a report that includes dates prior to the current month for a dashboard - So it needs to be automated (ie cant manually enter the date in)
I cant see how this can be achieved.
The best I can do is the Last # of Days (and put in a suitably large # value), but I get the current month up to the current day.
I was hoping grouping filters would allow you to "exclude" a group through "NOT",  so I could exclude the current month, however filter groups seem to only support "AND"  & "OR"

Am I missing something?
For example is there a value I could put into the date field like "now(month)" (similar to now() or Today commands used in excel/SQL) so I could use the "Before" filter?