Write a script with just one line:
In the pop up for specifiying the parameters for this step, refer to the email address field for the TO box.
Now go to your layout, enter layout mode. Select the field and use Button Setup... in the format menu to turn the field into a button that performs this script.
Note: When you turn the field into a button, you can know longer click into the field to edit it. You can still tab into it if it is in the tab order or you can use a different layout where the field is not set up as a button to edit the field.