Limiting databound picklist values using viewModel

Hi

I am trying to restrict the picklist values of a dropdownlist based on a formula on the quickcreate form.

I have a list of parking spaces associated to sites that I want to limit to only those available on a selected date.

The form has a calendar control  for the date selection, and a dropdown list to select the site.  When the site or date changes I want to change the list contents in the parking space drop down list to show only the spaces that are identified as unbooked on the selected date for the selected site.

I have  found the   kendo.bind($("#bookingSpace"), viewModel); function but it does not change the picklist content for the space selection dropdown.  

Is there a different way to alter databound picklist contents?

Thanks

Nick