In the report 2 add filter on column a.
In the operator option select +'is based on results of another analysis'+ ,
browse report 1 in the saved analysis,
select relationship is equal to any ,
use values in column a .
That is an interesting approach but it looks limited to using only one column, the matching columns in the two above reports were a and b - Is there a way to use both with this method or some other method ?