How do I dictate the order of preferred replica on a Always On cluster?
You can set the backup Priority to be higher on your non-DR node

By curiosity, why are you taking backup on the secondaries ?
There is some cases where your secondary could be out of sync with the primary (even if you set you AG to by Sync), for that reason, I usually prefer to have my backup done on my primary node.
Also, if you take the backup on the secondary node, are you also running checkdb on that secondary node ? (you don't want to end up doing backup of a corrupted secondary)