This can be done by creating a calculated field using the parameter similar to the following:
if index()<=[Top N Parameter] then 'show' else 'hide' end
Then, place this calculation on the view. Right click on the 'hide' member and select Hide. Finally, do the percent of total calculation--this will include all of the values because the values have been hidden not filtered out.
Hope this helps!
Thanks so much Tracy that really worked out perfectly.