Okay, guys, this is a pretty easy little hack, right here.
I have verified this works on an XR15 remote, which I believe is the latest. Remember, you’re programming the box, not the remote.
A search box will come up while you’re doing this; pay no attention to it, just follow these simply instructions:
Hit EXIT -> EXIT -> EXIT (EXIT three times, quickly and deliberately)
Type 0030 (this is where the search box will come up, ignore it)
Press the ENTER button (the button that glows white in the middle of the directional pad)
Your PageUp button will now fast forward 30 seconds, and your PageDown button will rewind 15 seconds.
NOTE: This will NOT work on Xfinity On Demand titles. It will only work on DVR-recorded programs and live (buffered) television.
Hope this helps some folks.