Is there a way to automatically add landfill under everything in a blueprint?

I have a bunch of blueprints that I want to have landfill under the buildings so that when I try to build on water it automatically fills in where needed. I have some rather large blueprints with lots of open area, so just plopping a blueprint into a huge area of landfill and then re-grabbing it would give me too much extra landfill. I looked at [Autotorio](https://autotorio.com/blueprint) and it doesn't have an option for it. I can do it manually with [Teoxoy's blueprint editor](https://teoxoy.github.io/factorio-blueprint-editor/) but it has trouble with my big blueprints. Are there better options to do this quickly or is there an in-game way to do it that I'm missing?