[Is] there any way to enable adhoc mode in JellyBean. WPA_supplicant hack isn't working.
Root your phone, then use root explorer and download this wpa_supplicant file. Rename the original to wpa_supplicant_backup and set the permissions of the downloaded wpa_supplicant to match the permissions of the original one.
I tested on Android 2.3.6 Gingerbread it worked like a charm - almost. Sometimes I have to turn off the and turn on the WiFi twice but it's not a big deal.