ST1100/1300 riders all find the same situation. Many buy extra key blanks and have them cut, and then cut off the key-head and glue on a plastic radio knob and just leave that "fixed" key in the panier lock on each side. I know those keys are not like our keys and not sure where you can get any of the CTX keys cut other than direct from Honda.
I prefer having to use the key for the latches. Keeps me from leaving the panier open/unlocked as I have been known to do on my GL1500. Once travelled down the highway from one town to the next, about 35 miles, with my panier hanging open while on a trip with stuff packed in there. I didn't lose a single bit of what was in there even though some was smaller loose stuff. And those were the same type of clamshell paniers as the CTX has... just a bit bigger.