Well you really can't. Best you can do is request them like you've done but it's not a simple task.
Add the fact that they are pretty useless at updating new songs anyway.
They secured the universal license and we're still yet to see Bon Jovi, greenday in the store etc..
First they need to buy a licnese to distribute the song via digital media (downloads) then they need to work on coding the track so it can be played properly.
It seems a real sturggle for them to get 20 songs a month out..
For what it's worth, Lady Gaga has at least 5 songs on the store & I believe thay are available in a song pack when the latest update hits so you save a bit of money buying the pack.
