It's nothing like training mentally, but there are a number of things I'd recommend doing off the bike to improve your riding. If you have a sedentary job, your glutes are probably not working well, so do some glute bridges. If you don't have great lower limb stability (can you stand on one leg without wobbling?), then you'll be losing efficiency through this, and are at more risk of injury too, so work on it.
Your core is key for cycling, so bridges are good to do at home (in an ad break if watching TV), especially side planks. Also when riding, practice holding yourself up with your abs (take all weight off your hands, though hold the bars loosely for safety). I'm working with a client in these ways, and his peak power is up by 20% after just three weeks.