It works! Just used it 20 min ago.
Procedure:
Sign up/register (Don't select or use any discount codes when you sign up)
Select the 2 x 5 meal plan (original box or veg)
Type in your details, delivery details, payment details etc and use the code: FBODRSD
The code will turn your $110 order into $1
Once paid and processed, go ahead and cancel the subscription
Extra Hack: Apparently you can use the same CC details on a new account (ie different email address) and it will work!
You know what would be great? A shopback on Ubereats this Friday afternoon.