The o/s rear door most definitely isn't the same as the driver's lock.
Tom's given you an offer of a working lock for the driver's door which I think you should take up.
Alternatively, I previously linked to this driver's lock:
FRONT RIGHT DOOR LOCK ACTUATOR MECHANISM 4B2837016 FOR AUDI A4 (B6, B7) A6 C5.
www.ebay.co.uk
which has definitely been fitted to an A2 in the past. It requires minor alteration to fit, covered in detail in this thread:
There is a method to finding alternative Audi parts; generally the part no in the middle stays the same, in this case 2837016, the first two as you probably know refer to the chassis (8Z) etc. For example, I bought parts for my R8 that were Golf & Audi A3, notably the clutch master cylinder...
www.a2oc.net
I was surprised you didn't go for that lock from the outset, given that the hard work (establishing how to fit it) had already been done.