I don't know if using the universal selector is appropriate, but I managed to make up an alternative with the following code.
Code:
$('html').keydown(function(event){
if (event.keyCode === 9)
{
$('html').animate({
scrollTop: $('html').scrollTop() + 500 + 'px'
});
return false;
}
});
Preview: http://pastebin.me/49dd9b1b4aa77
Also, just an idea, maybe make it so key + tab will scroll back to the top or when you're at the bottom and press the tab again, it'll scroll to the top.
Goodluck.
Edit: I've found that it doesn't work for Safari and Google Chrome (webkit) so here's the fix for it.
Code:
$(document).keydown(function(event){
if (event.keyCode === 9)
{
$('html, body').animate({
scrollTop: $(document).scrollTop() + 500 + 'px'
});
return false;
}
});