You can still bind another directory over /lib/firmware. Copy the existing firmware to a temporary directory, add your new firmware, then bind the temp directory over the /lib/firmware directory.

mkdir /tmp/firmware cp -r /lib/firmware/* /tmp/firmware/ cp -r my_firmware /tmp/firmware/ mount -o bind /tmp/firmware /lib/firmware 

You'll have to reload the ath module mounting so that it can pick up the firmware. Now any firmware you add to /tmp/firmware will be available to the system

Option 1

You can still bind another directory over /lib/firmware. Copy the existing firmware to a temporary directory, add your new firmware, then bind the temp directory over the /lib/firmware directory.

mkdir /tmp/firmware cp -r /lib/firmware/* /tmp/firmware/ cp -r my_firmware /tmp/firmware/ mount -o bind /tmp/firmware /lib/firmware 

You'll have to reload the ath module mounting so that it can pick up the firmware. Now any firmware you add to /tmp/firmware will be available to the system

Option 2

Add a firmware_class.path argument to the kernel command line to add an additional search path for the kernel firmware loader See kernel documentation

When the liveCD boots try this:

gentoo firmware_class.path=/tmp/firmware