Which FRC toolchain are you referring to? I'll assume you're talking about C++ as that's probably the one causing issues with a rootless environment.
First, I don't know why you'd want to keep System Integrity Protection unless you don't trust yourself. To me, it seems to be more of a "users are dumb and need to be protected from themselves" feature.
As far as workarounds, you could try putting the toolchain somewhere in your home directory. I'm not sure how the FRC official one works, but you can take a look at the debian packages
here or my
homebrew packages to get an idea of how to build it from source yourself if need be.
Lastly, homebrew by default will chown /usr/local to your user so that it need not be run with
sudo every time. This means that, once installed, it
might work with System Integrity Protection enabled. That said, installing it would probably require it to be disabled.
Personally, I would just disable it, so long as you trust yourself to be an administrator on your own computer.
Best of luck, let us know how it goes.
EDIT: You can also change the default install path for homebrew to be within your home directory, so if it doesn't work out of the box, that would be my go-to option; change homebrew's install path to somewhere in your home directory and use
my homebrew ports to install the toolchain.