You may be able to do this using a table calculation filter - i.e. LOOKUP(ATTR([DateField]))
The downside is the filter will only apply to the one worksheet, so on a dashboard with multiple worksheets the filter will only affect one of the worksheets and not all.
Thank you Andrew. This also led me to the Tableau KB entry about table calculations filters.
The thing is, after doing "LOOKUP(ATTR([Date]),0)" and moving it to the filters area, i get:
"The calculation Filter_Date can't be applied to a user-defined aggregate"
Ooops, i got it. Forgot to set the filter as continuous.