General :: Share A Large Number Of Files Into Chroot Env?

I understand that chroot is usually used to provide security, however, for my issue, security is a big don't care. I am very new to using chroot and don't fully understand how the chroot'd env works.

problem: Trying to use a vendor supplied cross compile environment. The environment runs as a chroot'd env and works just fine. I have a large number of additional modules that I wish to compile in the chroot'd environment. FYI, these modules are also (succesfully) compiled for other targets not using chroot'd env's. Copying the source files into the the chroot environment is not an option (don't have hours to wait for copies to finish and it would break the make system). Having them live in the environment is also not an option (the chroot build is a tiny part of the build process and we cannot revamp our entire source tree to accommodate it).

I am looking for a way to have the compiler in the chroot'd env have access to a path that is outside of the env and typically higher up in the same path that holds the chroot'd env. I have tried soft links (they don't work as expected). Hard links only work for single files and there are 10's of thousands of files that would need to be linked. I am not sure how I would go about exporting the additional files and then mounting the exported files in the chroot'd env (or if that would even work).