It's been awhile since I used Flexibility with Progression.....but within Macola ES, when you are in Designer, you right-click an open area of the screen, left-click Special, left-click Add Entry Field. You should get prompted with a message about adding the field as the next number in the screen set...just click OK.
The VBA-only comes into play on the properties of the new field....right-click the new field and then left-click Properties. One of the check boxes is for VBA-only. You can also change other "attributes" of the newly created field.
I always change the value of the literal that goes along with the entry field....this will end up being the object name within the Flexibility project. You can always hide the literal if you don't need it.
Enjoy!