Headunit Bluetooth help

[paulwoof]

Im looking for some help from the car audio guys or anyone that knows bluetoothy stuff, (im a tech newb at this stuff)

i have this headunit: http://www.amazon.co.uk/JVC-KW-R400-Double-Stereo-... in the car i just bought.
now reading the description it says it is bluetooth compatible and it has a bluetooth source on it but it is just compatible and it requires this £40 JVC adapter: http://www.amazon.co.uk/JVC-KS-BTA100-Bluetooth-Ha...

Now all i want to do is link my phone to play spotify through the cars head unit. im not interested in making calls etc.
So can anyone advise on best way to do this. I tried usb cable to phone but that only allows the phone to be used as a storage device, I believe a 3.5m to 3.5m cable should work, But i would like to do without a cable hanging around my gearknob if possible.

Would a cheap generic bluetooth dongle work plugging into front usb? http://www.ebay.co.uk/itm/USB-BLUETOOTH-DONGLE-ADA...

any help would be appreciated

[Ryanmt]

If the headunit has an aux in something like this should do the trick

http://www.amazon.co.uk/JUSTOP-BTR006-Bluetooth-Wi...

Your missing out on being able to control the playback via the stereo though so youll need to faff with your phone to skip etc. Might be worth spending a few quid and getting a stereo thats got it all built in?