Here is all I could find so far as a work around. I have checked the 2Wire configuration page but I do not see how to put the modem in bridge mode. I am using an Airport Extreme connected to my2Wire via ethernet as my wifi router so I do have another router available if I could understand how to implement this solution presented below. Perhaps someone more network savvy than me could come up with a procedure to implement this solution. Below is the quote from another discussion board (not an Apple forum) discussing the general 2Wire 2GB file limitation problem. The discussion quoted below is not referencing the AppStore download issue specifically. It is a general discussion on the apparent 2GB file limit for the 2Wire 2701 router.
"Yes, it does indeed seem like the modem is the culprit. I'm using the 2Wire 2701HG-D with the QT04-6.1.5.48 firmware update that was forcibly downloaded by Qwest a while back. I discovered that other people had had similar problems downloading large files with this modem after the firmware update.
I was able to get the download to work by setting the modem to operate in transparent bridging mode and connecting it up to an old Linksys router I had lying around operating in PPPoE mode. The file downloaded perfectly once I did that. It seems like the PPPoE capabilities of the 2701HG-D are flawed."