You could create the following calculated field within your workbook:
IF [Academic Period]="201130"then Date("1/9/2012") elseif
[Academic Period]="201210"then Date("5/21/2012") elseif
[Academic Period]="201220"then Date("8/20/2012") End
When you drag this field into 'Level of Detail', and then change it to 'Exact Date', it will appear in the ' add reference line menu' under 'Value'. Choose Maximum on top of that and then it should work. You might want to customize the filter, 'Academic Period' as well, so that it does not show the field 'all values'.
Hope this is helpful,