for a little more context,
here's a version of the attachment i made for a battery powered light - the white stuff is freshly 3d printed, it will be painted matte black. the bolt through the captured nut has a thumbscrew on the other side allowing the light to be easily removed for charging. but it's a pretty heavy light. would be way better to connect it to the bike's battery. obviously the part which the light slides into (which is an extremely tight fit, not going anywhere) would be made differently for a smaller wired light.
from below - the two black bolts are into the pair of embeds in the bar. there are no other holes. i could probably make a hole in one of the plastic headset spacers, but the wire will be exposed and coming out below the rotation of the bars.
here is what a previously finished version of the sp-connect mount looks like on top, it's very clean.
i'm leaning towards only using one of the bolts for the mechanical attachment, along with a complete layer of VHB tape on the mating surface. i'd hope the tape would remove any bending while the single bolt would be adequate for the "vertical" component of the load. and, of course, a light without a battery is a fraction of the weight.
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crazy alternative might be to electrify the bolts from the inside and embed some wiring channels inside the 3d print. not sure what the implications of power being present at the embeds and exposed bolt heads would be though. i can imagine with enough rain it might short across them.