A fast way to flash incrementally compiled kernels

In the following issue https://gitlab.com/postmarketOS/linux-postmarketos/issues/8 @pparent asks:

General question: So that I can work on this with most ease, can you tell what is the easiest way to recompile and flash on nexus 5 a modified version of the kernel (with just few modifications in some source files)?

Such a thing does not exist I think this is something that could done by pmbootstrap. The workflow is outlined below.

Set up envkernel

$ source pmbootstrap/helpers/envkernel.sh
$ make <defconfig>

Incremental compiles

$ make
# Flash the kernel

# Modify source code
# Incremental compile
$ make
# Flash the updated kernel

# Modify source code again
# Incremental compile
$ make
# Flash the updated kernel

# etc...

The step we are missing is a way to flash incrementally compiled kernels. What could be implemented in pmbootstrap:

Installing an updated kernel

1. Leverage mkinitfs to package boot image with kernel compiled in envkernel(?)
2. Possible methods to flash an updated kernel:
   a. Use flasher to install incrementally compiled kernel.
   $ pmbootstrap flasher flash_kernel
   b. Push boot image to device. Write boot partition with dd if=boot.img of=/dev/mmcblkXpY
   Dangerous: Easy to mistakenly write the wrong partition
   c. Package AnyKernel updater with the zImage from envkernel. Then adb sideload the package.
   d. Build kernel apk package from envkernel ???