I actually think I was reading on XDA that ad hoc support is not built in to Jelly Bean and while they are working on a workaround to get adhoc connections to say connect your Nexus 7 to your 3g phone they haven't been able to figure it out yet. Much of their work is based around using an app similar to those found
here.
However they HAVE figured out another way to get internet access through your phone through a bluetooth tethering app of all things that can be found at Google Play
here. Now you'll have to find the instructions yourself on the XDA site by searching around and if/when you figure it would be great if you could post it here for others to see if it works for you.
Thanks.
BFM.