When Channel 9 is turned off on a UA flight, I've found that a non-threatening (as if just joking) comment to a an FA like "I wish we had Channel 9 on this flight; it's a major reason I fly UA- no one else has it- and I was really looking forward to it" about 50% of the time results in Channel 9 magically becoming available - usually with an announcement from the Captain pointing out the feature and thanking us for our patronage. Too bad DL and the rest don't have this.