I have attached a patch which enables you to specify additional compiler config files to be used.
The main use case I have for this is buidling a spring-actionscript based project. Because it uses an IOC container a lot of the dependencies have to be explicitly included at compile time or it will fail at runtime since they are not included in the build. It is pretty easy to generate a compiler-config file for these projects that contains a list of all the classes needed at runtime by parsing or running an xslt against the xml context file - but up until this patch flex mojos had no way to tell it to use an additional config (or multiple additional config files)
It is used like this:
The additional config files that I'm using look something like this:
Doing the includes this way makes it possible to have a pre-compile task generate the list of necessary includes for projects that need it. I've written a mojo that does just that for the spring-actionscript based projects that I'm going to release once the ability to specify additional config files is added to flex-mojo (otherwise the mojo is not very useful)
It also adds in the -load-config+=(config path) to the flexbuilder options which will make this method of specifying include files more friendly to people who want to do both maven and flexbuilder builds.