Could you possibly make a package with entry for multiboot? some kind of "reference" package is here: http://www.mediafire.com/?t3mdemq1hj7v5ur (got it from NITDroid Wiki entry, file name inside this rar: "multiboot-kernel-maemo_0.3-1_armel.deb".

If you want to replace kernel-power, you should also consider creating a package that replaces package "multiboot-kernel-power" with contents:
/boot/multiboot/vmlinuz-2.6.28.10pali1 - your zImage file, but it has to have the same name as folder in /lib/modules
/etc/multiboot.d/01-Maemo-kernel-power46.item - multiboot menu entry, same as in my post here on page 8 of this thread
/usr/share/doc/multiboot-kernel-power/copyright (see this file in multiboot-kernel-power_0.3-1_armel.deb for reference)
/usr/share/doc/multiboot-kernel-power/changelog.Debian.gz (see this file in multiboot-kernel-power_0.3-1_armel.deb for reference)

And basically that's all to have a package for your kernel working with multiboot. Than, if one wants to install your kernel and use it with multiboot - just install kernel package, modules package, flasher package and than yours multiboot-kernel-power package