I have a similar setup in that my MBP 17" 4,1 has a replacement BT/WIFI. The two bits I needed to change for everything to work were the IOBluetooth.framework and whitelisting in the IO80211Family.kext for my board ID.
(CAT also says they were whitelisting in IOBluetoothfamily.kext, but I haven't been able to find where they were doing that).
You have to disable SIP to do the edits. Pretty sure you can re-enable SIP once you've completed them.
Not sure if you need the specifics, but I'll put them here in case others do.
For the SystemParameters.plist, you need to copy it somewhere else (make a backup of the original) - if you look at the file, you'll see the sections for the systems that DO support Continuity don't even have a "ContinuitySupport" section - so, just delete those bits for your card.
e.g.
<key>Mac-F221BEC8</key>
<dict>
<key>ContinuitySupport</key>
<false/>
<key>DID ProductCode</key>
<integer>18954</integer>
</dict>
becomes:
<key>Mac-F221BEC8</key>
<dict>
<key>DID ProductCode</key>
<integer>18954</integer>
</dict>
You need to be navigated to the path
(/System/Library/Frameworks/IOBluetooth.framework/Versions/A/Resources)
in terminal as well - so you can fix the ownership and permissions on the file:
sudo chown root:wheel SystemParameters.plist
sudo chmod 644 SystemParameters.plist
Presuming you have a Broadcom card for this next bit.
For the IO80211Family.kext, the whitelisting is in the /Contents/PlugIns/AirPortBrcm4360.kext/Contents/MacOS/AirPortBrcm4360 module. That's the file you need to hex edit and look for
mac- (board ID's) and change one of the existing values in each section to your board ID (zero filled with 0's to the right - so it would look like Mac-F221BEC800000000
There's actually two sections that your board-id must be in.
Once you search all the way down to "mac-phi-state", you're done. Save it.
(again, make a backup of the original, copy the IO80211Family.kext to your desktop, do the edits there and copy it back to S/L/E) - again, you need to be in terminal to repair the permissions to the file, then rebuild your kext cache (or use kext utility to do this work for you)
sudo chmod 755 IO80211Family.kext
sudo chown root:wheel IO80211Family.kext
sudo kextcache -system-prelinked-kernel
sudo kextcache -system-caches
Then reboot.
You can then re-enable sip, after the reboot (I'd make sure everything's working the way you want first)