This might be too outside the box and you would have to have the room for it, etc., but what about designing and building a specialized home gym as an extracurricular that could be done as time allows and use engineering skills?
I was watching American Ninja Warrior the other day (laugh if you must). One contestant was headed to the Ivy League. When he wasn’t competing, he was helping his engineer dad build obstacle equipment in their barn for him to use for training. I thought maybe you could adopt a similar approach.
Also, my kid’s school offers six courses per semester. About 2/3 of her courses are “high rigor” (AP) and admissions counselors have signaled that is sufficient.