Building multiple kernels with "make release"

Is it possible to build multiple different kernels and include them all in
a release image?  release.conf says so.  But from experiment, what I see is
that:

* release.sh does pass both kernels in the KERNCONF variable to "make
buildkernel"
* "make buildkernel" dutifully builds both
* BUT, "make installkernel" only installs the first kernel and ignores the
rest
* Only the first kernel ends up in the final image
* It's not really clear where an alternate kernel should go, anyway.
Probably someplace like /boot/kernel.debug , but release.conf doesn't
provide a way to specify that.

So is the "multiple kernels in release.conf" feature unfinished?  If so,
does anybody have a good idea about the best way to finish it?

https://github.com/freebsd/freebsd-src/blob/7045b1603bdf054145dd958a4acc17b410fb62a0/release/release.conf.sample#L32

-Alan