I’ve had many requests to support customising the newer (v4) Pogoplugs. Unfortunately I don’t own a v4 Pogoplug so could not create instructions for this device. However, I have since worked through the issue (over email) with a v4 Pogoplug owner after they got in touch via my contact form.
I’ve updated my original Pogoplug blog post to include support for v4 Pogoplugs (using external USB sticks) and also different BusyBox versions:
Let me know if these instructions work for you.