How to set multivalued Property to a group of check boxes.

Hi,I created one property with multi-valued enabled in the Properties metadata. This is visible in the properties of the xml form buidler.

If I create a combo box and then this property is set to property reference of the combo box all the values are appearing .

Now my question is how to set the value and property schema for the check Boxes with all the valuse in the predefined property.