The EFC for 30 second skip on Motorola boxes is 00173. !5 seconds back is 00179. The typical setup code is 1376 (01376 on remotes with the red OK/Select button.)

To assign these functions, choose a button (I'll use PIP Ch+ as an example)

1) Tap Cable
2) Press Setup until 2 blinks
3) Enter 994 (2 blinks)
4) Tap Setup
5) Enter 00173
6) Tap PIP Ch+
The remote should blink twice. Now tapping PIP Ch+ will advance the PVR by 30 seconds.