It is frustrating that there is so much in medical practice that we cannot control. I find it liberating to exercise influence when we can (even in small ways). Sure, the patient usually picks the pharmacy, but we have a say if we choose to. If a pharmacist provides lousy service, I have had no problem telling the patient "I would rather you pick a different one; we have had problems getting good service [or reasonable prices] from that one". I have done this (only after giving the pharmacy a chance to improve their service) and the patient is fine with it.
I am in an area where there are literally hundreds of pharmacies, so the patient can pick a different one with little inconvenience. That may not be true in a smaller town. On the other hand, if there are only a few pharmacies in town, I would think that each would be more sensitive to the requests of individual docs.
I am all for educating patients about the workings of eRx. This is the fallback position when the problem persists.