Realistically, I doubt any pedestrian bridge would collapse with one extra kilogram of weight, so, he just walked across the bridge without any problems.
If there was a strict 70 kilo limit, and he did have to carry the pieces on his person (not twirling around his head, or juggling, or any sort of other way people have come up with as a workaround), I think a several-day crash diet, shedding of clothing, or amputation(if he absolutely needs to get across) would be some of the only valid ways.
I would stick with the crash dieting and wait it out myself.
The upward force on the whirly-gig comes from the air it is blowing down. The downward force on the air is not all on the bridge. Since the whirly-gig is supported by the air, not the bridge, it’s not contributing its full weight to the bridge.
Unlike an elephant, if a helicopter flies over you, it doesn’t crush you. It’s weight is distributed over a wide area, not just straight below it.