japanpsyhic,
Although I have never practiced these techniques I get a really bad feeling about them. The usual admonition of 'If it seems to good to be true it probably is' comes to mind. The only realistic way to thicken a trunk is to allow the passage of time under good cultural conditions.
If you are limited, as you describe, about the best you can do is to pot your trees up as they require, this is common nursery practice.
or even chopping it,
Chopping a tree does not help to thicken it, it may help give the
impression of thickness as a shorter tree will appear to be more in scale. Actually any pruning only serves to slow development. It helps to give the tree taper and movement but this comes at the expense of trunk growth.
[url=https://www.evergreengardenworks.com/trunks.htm]This[/url] article will go a long way toward your understanding of trunk development.
Norm