Was alcohol involved in this ‘trick’ 😉
Living where you do and having easy access to higher altitude training is good and you should definitely try to do a few of your weekly runs at 10,000+ feet especially the long ones. Spending hours there will definitely help on race day. Sleeping a bit lower should allow you to recover well from the higher training days.
Pure speed will not be such an important quality to train so the fact that you will be moving much slower at 12k on these training days is not going to coast you on race day.