Nope, binary patching
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Speaking of, a slightly less permanent approach could be to just patch out the EVIOCGRAB, and do that on your end, since I assume if you grab it, Nickel then gets the shaft (easy enough to double-check with two different evtest instances, the first one not grabbing, while the second one does. That does require Nickel to be down, since it currently does grab ;p).
I think @frostschutz has some experience with that, IIRC.
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Otherwise, you could simply bypass Nickel, and boot into a custom app where you handle input as you see fit
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