I've been meaning to stick an 8x16 brick to the side of a cupboard to use as a key holder/hanger, where the keyrings are 2x4 bricks or short Technic beams. But I don't fancy gluing it. Double sided tape seems like a good idea, but under side of those bricks don't have much surface area.
I was surprised no-one had suggested Sugru yet. Here's one site with a few ideas that explains more:http://www.instructables.com/id/LEGO-sugru-4-awesome-projects-video/They've recently brought out a new version of Sugru too that apparently is safe for kids (the page I linked has a warning that Sugru is safe for kids one it's cured but that refers to the old formula).
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