Use RAWNODEFS with MEMFS on the same module

I have a library that uses emscripten, and I would like to add an option for the consumer to use MEMFS or RAWNODEFS.
I tried adding to the compilation `-lnoderawfs.js -lnodefs.js`, but the RAWNODEFS replaces the MEMFS automatically, on the following lines:

```js
// Wrap the whole in-memory filesystem API with
// our Node.js based functions
for (var _key in NODERAWFS) {
FS[_key] = _wrapNodeError(NODERAWFS[_key]);
}
```

Is it possible to import the MEMFS and NODERAWFS, but choose at runtime which one to use?