What can I use to increase efficiency of inductive wireless energy transfer instead of factory manufactured ferrite plates?
Are there any other options?


I would recommend you look at flexible ferrite sheets such as these: -



The relative permeability (\$\mu'\$) of a lot of them are good: -



If you are looking at 13.65 MHz (a standard) the purple graph indicates it has a relative permeability (\$\mu'\$) of over 100 with losses (\$\mu''\$) off the bottom of the graph.

Just google "ferrite sheets" and you'll find several different suppliers (MEC, Laird, Wurth, Ferricor) to whet your appetite.


  Could someone confirm if this DIY method really works or is this
  nonsense?


I really have no idea about this but, in particular, I would be concerned about high frequency performance. 13.65 MHz is a standard frequency used for wireless charging and that might be ruled-out without the correct ferrite dust.