Lightbulb!

Install “ES File Explorer” from the Play Store, and then open it.

Swipe in from the left edge to open the menu, and then click “Tools”.

Scroll down, and enable “Root Explorer”.

A dialog might pop up asking you to grant superuser access. Click “Allow”.

Enter your PIN if necessary.

Navigate to /system/. Click on build.prop.

Open it with “ES Note Editor”.

Click the 3 dots, then click “Edit”.

Add the line qemu.hw.mainkeys=0 to the end of the file.

Press the back button, then when it asks you to save, click “Yes”.

Navigate to /system/usr/keylayout/. We will need to edit the following files:

Generic.kl
gpio-keys.kl
melfas-touchkey.kl
qwerty.kl
sec_key.kl
sec_touchkey.kl

Click on Generic.kl. In the “Open As” dialog, click “Text”.

Open it with “ES Note Editor” as before. Change to edit mode, then comment out the following lines by putting a “#” at the beginning of the line:

key 102 MOVE_HOME
key 139 MENU WAKE_DROPPED
key 158 BACK WAKE_DROPPED

Save the file.

Follow the same steps for the rest of the files, but comment out the following lines instead:

For gpio-keys.kl, comment out the following line:

key 102 HOME WAKE

For melfas-touchkey.kl, comment out the following lines:

key 158 BACK VIRTUAL
key 139 MENU VIRTUAL

For qwerty.kl, comment out the following lines:

key 158 BACK WAKE_DROPPED
key 139 MENU WAKE_DROPPED
key 102 HOME WAKE

For sec_key.kl, comment out the following line:

key 102 HOME WAKE

For sec_touchkey.kl, comment out the following lines:

key 158 BACK VIRTUAL
key 139 MENU VIRTUAL

Exit ES File Explorer.

Open the Settings app. Under “Device”, click “Buttons”

Click “Backlight”, and uncheck “Illuminate Buttons”.

Reboot, and enjoy your shiny new soft keys!
NOTE: You will have to repeat these steps (with the exception of the backlight setting) every time you do a system update.