It's different than a Season Pass. First, it depends on which DVR you got. Comcast doesn't make DVRs... they just buy them from other companies. Most of their DVRs are Motorola DCT, DCH or DCX DVRs. Some, though, are from Cisco (Scientific Atlanta) and some are from Samsung.We have had Tivo for years but just got Comcast DVR. Can you do a season pass with the DVR?
Beyond that, something like season passes isn't a matter of the hardware, but rather the software. Even on the most common DVRs, the Motorola DVRs, there could be different software running in different parts of the country. The vast majority of Motorola DCT, DCH and DCX DVRs are running iGuide software. (A small number of them are actually running genuine ported TiVo software.)
Assuming you've got a Motorola DVR, and assuming it is running iGuide, the feature that corresponds to season passes is called Series Recordings. Detailed instructions for setting up Series Recordings can be found on page 38 of the user manual, which is available online (only, I believe): http://broadband.motorola.com/dvr/downloads/URMD2.pdf
A few notes about Series Recordings. It is very much dependent on the network you're recording providing accurate information to the program listings services. If the information in wrong, then you could miss an episode (if it is erroneously marked as a rerun) or get a lot of extra episodes (if reruns are all marked as new). Also, it isn't as smart as TiVo, so especially for cable shows, you're more likely to get more episodes or less episodes than you'd expect.
There are also some insidious problems with canceling episodes of a Series Recording, if you happen to have two series recording at the same time. It often only lets you cancel one of the two.
You might think to try to fix some of these problem by setting up manual recordings of shows for which you have a Series Recording set up. Don't. That really confuses the software, and folks report that sometimes it ends up recording 12-15 hours straight, and then the box locks up at 4AM.