You have to careful and do it in a ventilated area, preferably outside, but gasoline works on anything. Take a rag and wrap it around your index finger, wet the tip of your finger with gas and rub away the adhesive. Wash gently with dish soap and wipe dry to get rid of the residue and gas smell.
After looking at your user manual I see a Bluetooth powered sub with a standard AC cord. This should work with other Bluetooth devices provided JBL hasn't done something proprietary with this system. See https://www.groupon.com/articles/how-does-bluetooth-work for a fairly good explanation of Bluetooth. Then, before buying anything, I would call JBL tech support and rule out the "proprietary" possibility (+44 161 222 3325).
Cheers!
Find the Play / Pause and DOWN Volume buttons. The Power button is in the middle of the button pad, and the Volume DOWN button is on the right
The Flip 2 would then enter hard reset. The lamp in the power button would flash white a few times.