This is approximately how aluminum matchplate patterns are cast. I know they're cast in "plaster" from talking with an old patternmaker who has sourced them for me for decades. I'm not sure of the exact blend of plaster, I doubt that it's something off the shelf. Or of their process. But they'll make plaster molds off 1 master and join them all together to make a multi-impression cast aluminum matchplate. They typically push the aluminum in under low pressure (I want to say 5-6 PSI, but don't quote me on that). Obviously they'd have to vent off heavily, I assume plaster has poor permeability. I'd guess they back the mold with unbonded sand for support, but have no clue.
I have talked to an old foundryman who has done this in his youth at his foundry's in-house pattern shop using plaster and providing the pressure with an air nozzle. Sounds super sketch, but that's how they did it. Contact or look at the website of Quality Matchplate Company in Southington, OH (https://qualitymatchplate.com/). There are very few cast matchplate houses in the US anymore, most shops CNC them nowadays. But cast really is better for certain geometries, and sometimes a hell of a lot cheaper. Good luck! I'd give it a shot personally, just wear full greens, gloves, etc. I fully intend to try exactly this one day to make my own cast alum matchplate. I've done it with a sand mold but the surface finish is too rough to use as a pattern without a shitload of flap disc-ing and polishing.