Do you have the ML Stereo or the standard one? If the standard one, people have replaced their whole console with FlyAudio which will give them the full functionality e.g. onscreen display, GPS etc etc
If you do have the ML system - I also have this problem and have looked at alternate (besides plugging in the audio cable) - I read somewhere one of the alternate is to install/purchase something like a BlackBerry Music Gateway.
The BlackBerry Music Gateway is one of those must-have mobile accessories. It's small and versatile, allowing you to wirelessly stream music from your BlackBerry or other phone or tablet (Android, iOS, Windows Phone) to your traditional home and car audio systems.
Now you can enjoy the music on your mobile device through the power of your home or car stereo speakers.
Wirelessly play the music on your smartphone, tablet, or computer through your home stereo or car stereo using the BlackBerry Music Gateway. Just plug the BlackBerry Music Gateway into your stereo system, and pair it with most BlackBerry using Bluetooth connectivity or NFC technology, then fill any room with your music. It’s really that simple. You’ve got full control over playback, change tracks, volume, and play or pause because most BlackBerry is your remote control.
Wirelessly play music from:
Bluetooth enabled laptops and personal computers
Bluetooth enabled smartphones
Bluetooth enabled tablets
Connect BlackBerry Music Gateway to:
Bookshelf or computer speakers
Stereo system
In car stereo system
MP3 Player docking station
Features:
Connect via Bluetooth or simply tap to connect your NFC enabled device.
Compatible with any smartphone, tablet, laptop, or desktop computer that's A2DP enabled
Additonal Informartin:
Smartphone, tablet or device must support A2DP and AVRCP Bluetooth profiles
Smartphone must support Near Field Communication (NFC) for tap to connect feature. (NFC technology is not enabled for all carriers. Please check with your service provider for availability).
Connect using the RCA or 3.5mm auxiliary cables included in the box
Includes:
Music Gateway
3.5mm to 3.5mm cable
3.5mm to RCA cable
Micro-USB charger