For the MBP you need a BCM94331PCIEBT4CAX chipset - the one you have in your 2011 MBP is BCM94331PCIEBT4AX. You can open the computer to double check but this is probably it. I got mine on ebay from a 2012 MacBook Air.
Once you install the hardware you need to hack the .kext files, the tutorial is here:
That's it, everything works and this mod is +- $50 with shipping.
For the iMac, we need to figure out what chip with BT 4.0 LE is compatible, the rest is only about modifying the .kext files.