It can be done, and I have done it!

I have a Cricket wireless Lumia 640 with continuum mode working.

Follow the directions here:
http://www.windowslatest.com/2016/12/02/enable-continuum-support-lumia-phone/

I have mirrored the files here: Continuum.zip

Some notes:

1. After you install the Interop Tools app, you may need to reboot the phone. Before rebooting, I encountered crashes when attempting to open the INTEROP UNLOCK menu

2. You will probably need to first “Restore NDTKSvc” and reboot. Then the other unlock options will work

3. The directions include a tool – iutool.exe – in the i386.zip that allows for installing cab files on the phone. This tool is touchy, and is version specific. IF YOUR PHONE DOESN’T REBOOT ITSELF, THE TOOL DIDN’T WORK.
– Make sure phone is configured for developer mode
– Make sure phone has recent OS update – I believe the instructions were intended for the Anniversary Update.

When I first tried it, the tool immediately failed with an error. This probably means the tool couldn’t figure out which phone to update.

To resolve this, detach the phone, open the “Devices and Printers” control panel (search for it in the start menu). Remove any windows phones in the list. Reattach the phone, wait for windows to finish detecting, and try the command line again.

Next if it uploads the update but then fails, you may have the wrong version of iutool.exe.

I got the latest Phone updates for insider preview, and was able to successfully install Continuum using the version of iutool.exe here:

http://forum.xda-developers.com/showpost.php?p=68459157&postcount=13

(Mirrored here: WP_CPTT_NT-x86-fre.zip

The msi installer places the executable here: C:\Program Files (x86)\Windows Kits\10\Tools\bin\i386

When it works, the phone will reboot itself, you will see gears, etc. Even though the instructions say you may see an error, I did not when it worked.

—

Now I can use Word, Excel, etc on a Miracast connected display with a Bluetooth keyboard and mouse. If I were desperate for some spreadsheet or word processing action and all I had was the phone – I can now make it happen. When Continuum is enabled, your phone works like an input device for the TV, so you don’t technically need the keyboard and mouse.