How about creating calculated field
if measure <> "S16" then "Present" else "Past" end
and then create a hierarchy of Present/Past, Measure
This way you will have drill-down option to see present/past split with possibility to display details of the present.
Either you can create a calc field as suggested by Maciek or just create a group on your dimension.
Some useful links regarding group.
Let me know If this help.
That's good approach when selection is pretty static. using calculated field can benefit in more dynamic situation (for example when using parameter to set 'what is the present').
Thanks for both your responses. Sadly the end user wanted to retain the filter and just add into that Filter the On Sale option.
I have worked around it by adding a filter previous to Season which is a Past/Present and then filtering the Season by relevant values only. This is the best workaround I can think of.