I have a HP 840 G3 that was donated to me to Hackintosh, currently running High Sierra 10.13.6. This should work for the 840 G2 and you may even have more luck with the 840 G1 with the WiFi that PCIe.
My method to install OS X on the SSD from a working real Mac via SSD to USB converter. I then install Clover and add my kexts ad set the config.plist
SD Card reader
Video - screen looks better in OS X then it does in Windows 10
WiFi and BlueTooth working OOO using the below hack
Battery status with Rehabman's DSDT patch
Sounds - using VoodooHDA
Microphone - cannot turn it off or mute
Keyboard backlight - controlled though BIOS anyways
touchpad - using VoodooPS2Controller
USB3 - this laptop has two on board only and I haven't test them using the docking station
Ethernet - using IntelMausiEthernet
Sleep - kind of, closing the lid doesn't go to sleep but goes to sleep over time.
This laptop does not have a Webcam - enterprise model.
Finger Print device
For me what keeps this from being a day to day usable laptop (Mac Book) is the WiFi + Bluetooth, not having battery percentage could be an issue later though.