I wonder if it wouldn't have dripped so bad if it was warmer, purely me just guessing though. I'm not familiar at all with the grills on these cars, but yeah of you can't get behind it, your idea sounds like the next best go-to. Worst case scenario you could always feed a few black zip ties through the mesh for mounting. That's what I did for my civic, just with the coroplast on the backside of the grill.
Post pics when you're done if you can, it may help others with ideas when they try to figure out how to do it.
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