From a FAQ page I don't know if it pertains to the 4500, though.

"3. Can ReplayTV automatically skip commercials?
No. You have to use the QuickSkip button to skip them. QuickSkip skips ahead 30 seconds instantly. Believe me, you really won?t mind
that much. Also, beginning with version 3.0, you can enter a number and then QuickSkip to skip ahead that many minutes. For instance, 2
+ QuickSkip will skip over a 2-minute commercial break automatically. You can also use this method with Instant Replay to go backward
that number of minutes."

DirecTiVos have a backdoor that will do a 30 second skip, but then you lose the function to jump to a 15 minute index if you enable it. I use the 30 second skip all the time...