howster-
it kinda depends on what kind of recording you're doing. Is it solo piano? That's the most critical and diffucult to do well, but given whatever circumstances are given, hopefully you'll get good resutls.
If you're sure you're gonna use that particular upright, then yeah. Pull it away from the wall and let the kid get used to playing it in that position for a few days. It'll sound different than he's used to. Usually for live situations, you would mic the back like ametth said. You actually get more sound there than you do from above the lid (and it's a clearer sound). The back of the piano is actually the soundboard.
IF the kid is going to play without music, you also have the option of taking off the front of the piano and micing from that side.
There are SO MANY variable when dealing with a piano. You'll have to try a few different things to really know what's best for your situation.
If it's classical piano AND you can take off the front cover, I'd start out by putting the mics above his shoulders. You'll have to experiment with distance depending on the room and sound you want, but generally you don't want to get too close for classical piano.
