Leg day, done.
It's interesting, writing down my "dilemma" seemed to help my rational brain win. I also used an old trick from Duhigg's book, The Power of Habit (make your kids read it today!):
"I'm not actually going to do legs, I'm just putting on my shorts." Lizard brain doesn't react.
"I'm not actually going to do legs, I'm just warming up with light, painless weights." Again, no reaction.
"I'm not actually going to do legs, I'm just going to do a couple of reps with this weight." Hmm.
"Hey, that wasn't bad, let's keep going...!"
I've used an old martial arts trick that implies a greater penalty for non-compliance than compliance

I've been running about 15-20 miles a week now. Probably for the last year and a half, gradually increasing distance with some off days built on speed. The knees have lodged a formal complaint but thus far, they've not refused to comply.
Neighbor saw me a week back and said "see you running all the time. You gettin' ready for something?" I looked at him thoughtfully and said "old age."
He nodded sagely.
I turn 50 in 5 months.