PhyScroll is a Cydia tweak that will allow you to use either your accelerometer or volume buttons to scroll down pages. You will need an activator option to enable this like "Hold on Status Bar". After you are in Safari and have enabled PhyScroll, scroll with the option you chose in the settings. You can set it to use one or the other as well as both. The volume buttons make scrolling simple, easy, and fun with this tweak while the accelerometer could get annoying. PhyScroll will disable itself as soon as you physically touch the screen or press home. The settings will also allow adjustment of the scrolling sensitivity for both modes. You can find PhyScroll in the Cydia Store for $1.99.