There is BMW special tool that will allow unlocking of the magazine. I could try to find the part number for you as I do not think it is that expensive.
However, in most cases when this occurs the cd changer is usually defective and needs replacement. It might be worth having the dealer remove the magazine. If you stop in to the service drive sometimes a helpful service writer might even be able to get the tool and try to remove the magazine for you at no charge. At that point you can assess if the the cd's are stuck or if the cd changer is defective.
If you would like the part number of the tool please let me know. I hope this information is helpful. Please accept and let me know if I can help you further. Thank you.
The part number is XXXXX 1 170. This tool is designed to slide in and unlock a stuck magazine to prevent having to replace the entire cd changer. I hope this info will help. Thank you.