I found a lampshade holder with a broken lamp socket, decided to repurpose it with an energy-efficient G9 LED bulb (4W with same light as an old 40W incandescent bulb), but all I could find on eBay/Amazon were the bare socket holders for the bulb only. None would fit the purpose and mount onto a lampshade or lamp base.

So here it is, a 18mm ID (30mm OD) block for those ceramic G9 bulb holders.

The small ceramic holder fits snug inside, if your printer is dimensionally correct there will be no need to use further fixings, just press the ceramic holder in.

If the fit is a bit large you can use the two small holes inside (m2.5 screw), or use high-temperature JB-Weld or similar Epoxy glue to keep it all in place, although this would be a problem if one day you'll have to replace the wire.

**********************************
One word of advice: the G9 bulbs run on 220-240v so make sure you do know what you're doing!
Use quality wires and do not leave any bare wire exposed
**********************************

FYI, those bulb holders as in the picture, do only require to have 3-5mm of wire stripped and pushed inside the holder with no soldering or screws to tighten. 

The fit is safe but you have to make sure the main wire is held properly with the lamp base you're going to use, if no means of holding the wiring are present in your mains lead, please consider using hot-melt glue, zipties, or similar means to make sure you can't pull out a live wire by accident.

The bottom side of the block has an internal M10x1 thread to fit most common threaded stubs. Or you can drill smooth +JB-weld/Epoxy.

Inside the block there's a 5mm hole that goes all the way through, to run a 2-core electric wire.

On the top side there's an external M26x1.5 thread, with a large nut, to hold a lampshade. An additional collar can be printed to act as washer/spacer if you need it.

The version with a collar (for better hold of the lampshade) will need proper supports when printing.

This bulb holder must be printed with ABS, or PETG or Nylon, do not use PLA due to its poor heat resistance. 
Print upside-down and use supports, I use 3.5mm pillars and removal was very easy.

Print Settings

Printer Brand:

FlashForge

Printer:

Creator Pro

Rafts:

Yes

Supports:

Yes

Infill:

30% or higher

Filament:

Polymaker ABSD or PETG or Nylon, no PLA!

Notes:

Do not use PLA due to its poor heat resistance

Category: Replacement Parts