If you have a vase or bottle that has a cork or wooden top to support the lampholder then you may want to try this fixing method.
You will need a 10mm hole in the cork or wood then add a Allthread rod held in place with a washer and nut on the bottom and the top. Leave about 6mm of thread sticking out the top for the lampholder.
You can add a nut cover to the top nut to cover it before adding the lampholder.
Pick a 10mm entry lampholder for the top of the allthread rod.
The flex is then fed through the side hole and a cord grip is added to stop the flex from being pulled out. Add a grommet in the allthread to stop the flex being damaged before wiring the lampholder. Make sure the flex is protected where it passes through and cant get damaged.
You can use a hole grommet here.