You could try to solder the leds to a ribbon cable that could take power from the battery, like other mods for the iPhones, if you had a cable like so from a broken mod kit.
=== Update (03/05/2019) ===
Run a jumper wire from the logo to PPLED_OUT_A that drives 20volts to the LEDs should work.
You could try to solder the leds to a ribbon cable that could take power from the battery, like other mods for the iPhones, if you had a cable like so from a broken mod kit.