My method for hacking my brain is wakeup exercise. Finding a short exercise which I can do faster than I can talk myself out of it. I started with 5 pushups. That's all. A tiny number, 10 sec exercise which I do as I get out of bed in the morning.
The important part is not to "push the envelope" or whatever. The amount of exercise should be small enough that it doesn't bother you. And only do the exercise today. Don't think about yesterday, don't think about tomorrow. You only have to exercise once. Today. Easy. 10sec, 30sec, whatever. Then move onto whatever weird and cool shit you wanna do with the rest of your day knowing that you have exercised.
I feel like I'm cheating, cos it's so simple yet so effective. I now do a lot more than 5 pushups, but the concept hasn't changed.
Oh and as mentioned below, rock climbing/bouldering is fucking great. Go hang out at a gamified problem solving gym and you will exercise til you wish you could make yourself stop.