Dear Jbouchard,
You did the right thing by being honest. The last thing your Dad would want is to recover from the transplant, and feeling healthy, watch you descend back into addiction. Your transplant center considers your health a higher priority than your Dad's, and has to protect you. Your willingness is a great gift to him!
Truth be told, there are too many stories about recovering addicts who relapse after surgery. So elective surgery (which includes donation) is a huge risk.
Now, you can ask for a meeting with the transplant coordinator and or psychologist to discuss. When I donated in 2011, an iv drug called Toradol (not to be confused with Tramadol which has abuse potential) was used together with opiates for post-surgical pain relief. The thing about Toradol is you can only use it for a little while, it wreaks havoc with your digestive system. Anyway, the nurse told me that the use of Toradol significantly reduced the need for opiates in donors. But I don't know if anyone has ever donated without any opiates. But you could ask?
love, elephant