You can paste the following code to the console to scroll up/down using the a/z keyboard keys. If you want to set your own keys you can visit this page to get the keycodes
function KeyPress(e) {
var evtobj = window.event? event : e
if (evtobj.keyCode == 90) {
window.scrollBy(0, 100)
}
if (evtobj.keyCode == 65) {
window.scrollBy(0, -100)
}
}
document.onkeydown = KeyPress;