How to source additional file when launching bash

bash --rcfile <(cat rcfile1; cat rcfile2)

works just fine and requires no modifications anywhere.

Okay, so you want to run the user's normal .bashrc, followed by your own script, and you want to trigger this behavior in the way that bash is called, correct?

The call:

/bin/bash --rcfile myscript

First line of myscript:

source $HOME/.bashrc