How can I add dynamic file path access ability to emscripten's current File api?

I've noticed emcc's `-lworkerfs.js --preload-file` can only build a fixed file set,
However i need the wasm C++ code fopen can open any local file path (with potential support from server side)

https://emscripten.org/docs/porting/files/Synchronous-Virtual-XHR-Backed-File-System-Usage.html#synchronous-virtual-xhr-backed-file-system-usage says can use `FS.createLazyFile` api to create a mapping from a virtual wasm fs path to server side url path, but documentation says MUST used with --pre-js option.

Which means, --pre-js inject code is run at the begining of worker thread? Can I call `FS.createLazyFile` Just-in-Time to worker thread (before wasm C++ fopen run), in that case, I can support dynamic file path access...