Reviving an old thread to provide information.
Programming a key to your BMW's CAS will cost you money, regardless if you DIY or pay someone to do it. Nick has chosen to purchase genuine tools of good quality after initially messing around with some Chinese ones. However, there are tools for you to DIY which run in the $200 range for chinese clones and the process takes 15 min.
1: It's FAR easier to program a virgin key than a 'used key'. Virgin keys (chinese) are $15 USD on Aliexpress or from a key wholesaler.
2: A used key will need to either have the transponder de-soldered and a new one soldered in ($4 per transponder chip) OR you can purchase a PCF79xx Unlocker, or Xhorse VVDI PROG Programmer, and fiddle around with that to erase the data from the transponder. As you can see, you're better off buying a virgin key!!!
3: You can use HiTag2 to use prep the key and create a 'new key' file for use in BMW Explorer/EF Scanner Full OR used to write data back to the key if you've done a CAS dump and have the ISN key.
4: With a battery tender/charger on your car, use EF Scanner to program the new key to the CAS.
Here's how: