erlang embedded into C

The easiest way would be to just launch it as a separate process, and then use stdin and stdout to communicate. Just reading the docs of whatever platform you're targeting will let you know how to do that.

The only sane way to do this is to load the C code from the Erlang VM, not vice versa.

It's not possible out of the box, but since you have access to the Erlang source it's clearly possible to do whatever you want if you're willing to spend a lot of time modifying the code. It's not a good use of your time to go down this path.