My laptop has no mouse and the Win 8 touch screen doesn't seem to work so well with the small thumb marks on the browser columns. I have to point and click with the touchpad to scroll and it's not very user friendly or smooth.
It would good to add support for a pageup/pagedown and arrow key for scrolling in the next update. That's a fairly standard option on most preset arrangements.

Moved to feature request.
In the interim here is an autohotkey script which adds the requested feature to Rapture Pro

SetTitleMatchMode RegEx ;use regular expression pattern matching for titles
#IfWinActive, Rapture Pro*
PgUp::Send {WheelUp 20}
PgDn::Send {WheelDown 20}
Up::Send {WheelUp}
Down::Send {WheelDown}
#If