So this is not a fix, but there are devices that can basically take in an HDMI connection and output the same, but they allow you to inject CEC control as well as control and limit what CEC control is coming in. You have the option to allow CEC control to pass through or decide what you want to turn off. The coding for this is very simple and can be found online, you can basically just copy and paste and program it in via python2, Java, simple notepad text, etc... This actually would solve two issues, you could turn off the close captioning as well as allow the Roku to control more, for example when we were doing our testing we programmed one of the boxes so when the Roku received a button press that would wake up from sleep mode, it would send the on command to the display.
