Building a gzip'd kernel instead of lzma

Dear All,

I've got a bunch of Netgear WNDAP360's that I'm trying to put OpenWRT on.

The way this device works is that you need to put the kernel and then the rootfs on manually via uBoot first. See

Trouble is, the newer vmlinux.bin files are compressed with LZMA which my version of uBoot doesn't support. At the moment, I need to copy over OpenWRT-15.05's kernel and rootfs image, then sysupgrade to the latest.

Which part of target/linux/ar71xx/image/ do I need to modify to get a GZIP'd kernel instead of an LZMA'd one?
This line here looks promising, but it's not obvious to me:
$(eval $(call SingleProfile,AthGzip,64k,WNDAP360,wndap360,WNDAP360,ttyS0,9600,$$(wndap360_mtdlayout),KRuImage,65536))

Or is that the wrong file to play with?

Many thanks,