I found a solution to get around the problem, not very correct but it works.
I start by creating a folder "Barre" and then a sub-folder "I". (The choice of the name "I" is not insignificant)
I put my shortcuts there.
I create my toolbar.
I move it to the right place.
Right click on it and I keep only the title.
Finally I lock the taskbar.
Now with SkinStudio :
I create a font of size 1, named in my case "Mini - Arial".
Then I will apply this font here (see image)
Here is the result.
The icons are a bit off but I don't have anything better.
Thanks to everyone who helped me @basj, @SimplexDesigns etc...