How do I enumerate firmware used by compiled-in drivers?

[Michael Conrad <mconrad@intellitree.com>]

Hi, I am trying to maintain an initrd for a homebrew Linux distro. I'm 
having a problem where kernel modules are gradually shifting from 
linux/firmware to /lib/firmware, which breaks my initrd (which currently 
uses CONFIG_FIRMWARE_IN_KERNEL).  I am looking for a way to extract a 
list of needed firmware files from my compiled kernel so that I can 
include them in my initrd.  I want to automate this so that I don't have 
to fight it on every kernel upgrade.  A helpful fellow on freenode 
#kernel pointed out that modinfo contains a list of firmware names, but 
didn't know any way to find that information for compiled-in drivers.  
Is there any way I can do this?

More context:

I have an initrd, so I'm ok with the idea of switching from 
firmware-in-kernel to /lib/firmware.  However /lib/firmware is 57 MB and 
contains many firmware files which aren't even used by Linux 3.10.17 or 
by my configuration.  I want to include only the ones that the kernel 
might try to load.

I want to support most popular network and storage chipsets, plus a few 
specific less popular ones, so I have lots of drivers selected (some 
modules, some compiled-in) and I don't want to be surprised when a 
driver (like bnx2) decides to switch from an in-kernel firmware to a 
lib/firmware file.  I want my kernel-build script to search for and 
include these AUTOMATICALLY, because there are too many to inspect them 
by hand each time I upgrade.

Does anyone have advice for this?

Thanks in advance.
-Mike