^^^^ yes, a pop can wall is about 0.1mm. I measured this when I needed to use a 26mm stem clamp with a 25.4mm bar. It worked, but it slipped a couple of times so I eventually replaced the stem with a 25.4mm version. The bar end shifters shouldn't have much force on them at all, at least very little compared with a stem clamp. A shim should work just fine.
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Dale, NL4T