I used to have this DVR through a non-Comcast cable company as well. And I had the same problem you are currently having with not being able to program your non-Comcast remote using the instructions people gave for Comcast units.
I believe that the 30-second skip function is available unless your cable co disabled it. The problem is that your remote doesn't know how to tell the receiver to do it.
I actually ended up going to my local electronics store to buy a One-for-All remote (I can't remember the model number). I then programmed that remote to do the 30-second skip and used it to "teach" my universal remote the command. This was the only solution I could come up with. But I returned the One-for-All remote. So it cost me nothing.
Not the most ethical solution I know. But I couldn't figure out any other way. And I didn't want to drop a lot of money on another universal remote. Do a Google search on (motorola 30-second skip one-for-all) and I'm sure you will find the exact model remote to purchase.