Hi Bahrom,
Here's an idea: change the width of the date picker control to be just large enough to show the datepicker button (~25 px) using datepicker properties. Then, add a read-only expression box (calculated value) to your form just to the left of the datepicker button and set it up to read from the datepicker field. You can format this as a date by right clicking choosing properties, etc..
When user clicks datepicker button, it will change the date but they won't be able to type it in.
Hope this helps!