Reporting Services :: SSRS 2008 - Calendar Type Parameter Input

I'm modifying a report that uses a date parameter as a report filter. The original report had no restrictions on what dates may be entered, so it displayed a neat Calendar picker tool for use in selecting the date for the parameter.

Thing is, this new version needs to have the dates limited to only those available in the source data. So, when I provide a query to describe the available values in the parameter properties window, instead of the nifty Calendar picker, I get a texbox dropdown list. [insert sad sound here]

I was hoping that it would still provide the Calendar picker, but with available dates highlighted in bold or some color or the unavailable dates greyed out, something along those lines; not an unimaginative dropdown list. To define the available values, I use a very simple query;

SELECT DISTINCT Load_Date
FROM Census
ORDER BY Load_Date

Is there a way to get it to display a Calendar tool rather than the dropdown list, if the parameter is given a list of available dates?