In the same way that CyanogenMod does? Around the time of Jellybean's launch, Google released the PDK which made it easier and less intrusive to overlay the Android source code. As a result alpha builds of CyanogenMod 10 were in the wild before the Nexus S (or any branded device) released a Jellybean device. In fact, HTC still haven't even managed to get Jellybean on to their current flagship device. The only people stopping/slowing-down hardware support at this moment in time is the OEMs.