Given the type of people that we are targeting here I think that helium blow-up dolls are are a bit of a waste, especially considering the scale that we would need to perform this on to actually make it somewhat believable. Better would be to use hydrogen, its soo much cheaper than helium, has better lift, and is not a limited resource. Along with that a custom order of human shaped and roughly human colored (with painted on clothes patterns) balloons would work better. Likely a lot cheaper if done at larger scales, blow up dolls are made of tougher material than your average balloon. This would also allow for the pursuit of more sustainable materials given that we are just sort of releasing this stuff into the sky.

There is also a matter of making it realistic. If we are limiting to maybe one city then its best to create some devices that automatically release them on timed schedules. load these up with a handful of people balloons each and let them release with increasing frequency throughout the day. Should be a bit more convincing and gets a bigger effect. For cleanup we already filled these guys with hydrogen, so why not just light them up. might make for a good effect and leave less waste to be examined, making it more difficult to prove that this is not a rapture event.