I just ordered the 4 Pieces Original Recipe ADD ON and nothing else and it worked like a treat. Considering 5 pieces is normally $12.95 (or $2.59 ea) this is a grand total saving of $3.41 (4 x $2.59 = $10.36)
The ADD ON options are found under the Menu Hacks section in the app.
You can also get the 5 Original Tenders ADD ON for $6.95 which normally directly goes for $9.95, a saving of $3.00.
I checked back through past deals and I found that something similar has been posted but in both deals, they mention the option is under Shared Meal and it does not come up every time so I think KFC has since updated how this works.
Sorry QLD friends, apparently this does not work for you :(