Seems like it should be possible to solder an eUICC chip to a SIM-card form factor board and use it with OpenEUICC. [1] Somebody is even selling those pre-soldered on Taobao: https://shop104192953.world.taobao.com/
Later in that thread, somebody also reported that OpenEUICC works with eSIM.me's cards, too. If you have one of these, can you give it a try perhaps?