I do a ten-minute procrastination dash when I first get in before even taking my coat off (extra points for keeping your iPod on from your walk!), so I don't have chance to get distracted or realise how tired I am. This is enough to get a couple of bits out of they way (take the bins out, clean the sink etc.), so I can then
a) enjoy guilt-free the fixed amount of time to blow of steam that another answer suggests
b) focus on the real productive (or fun) stuff I had planned for that evening without fussing over mundane household chores to the extent possible.
To apply it to your keyboard practice example: maybe use those enforced ten minutes to give yourself a taster of an interesting or exciting challenge you want to get to grips with, then leave some water in the well so you're keen to come back after a break, having already done the hard part of starting.
You might also find this extension of the aforementioned procrastination dash technique useful in itself to make the task of starting on something productive after work feel less daunting.