First I tried with a beer can, then I bought a VO handlebar shim and tightened the bolt as hard as I could but given enought time the whole system will still loosen.
You anticipate that the beer-can fix will eventually fail
26-25.4=0.6, so use 0.3mm shim stock, which is what Nitto's pieces offer.
I fail to understand how my use of the past tense induced you in believing that I yet have to try either the beer-can or the shim solution.
Anyway it's not a big deal and me being the foreigner, maybe I just have to review my grammar.
I also doubt that there can be much of a difference between the Nitto and the VO shim so I will refrain from spending 15-20€ in the former (yes, that's the price I would pay to get it, skyhigh)
The alu foil wrap could be a good idea, I'll give it a try.