The question is if left and right "page forward" buttons have the same or different button code or not the same.
I used to use that linked LounchPad script to remap two buttons just next to D-pad (I think it was Delete and Enter or maybe Sym instead of Enter) that I needed the least, in order to avoid spreading of the hairline cracks in plastic that my Kindle 3 had i both bottom corners of the screen.
Edit: IIRC @seaniko7 also posted a custom kernel or something like that with some similar type of buttons remaping.
Edit2:
Here it is. It had space button as page forward