Use the Set Session Value behavior for each form element.
On the server behaviors panel, click the plus button and select WebAssist -> Cookies -> Set Session Value
For the trigger, select any form post, For the value, click the lightning bolt, expand the forms collection and select the first form element in the list. Set the name to the the same as the selected form element.
repeat this for each form element.
now in design view, select the first form element, in the property inspector, click the lightning bolt icon next to initial value (For checkboxes or select lists, click the dynamic button) and select the corresponding session variable.