Yes that should be possible. You could use this as a starting point: https://www.mobileread.com/forums/showpost.php?p=3812831&pos.... With that you can wait for the 'goingToScreenSaver' event and then write your dashboard to the screen.

There are some minor downsides though. If you keep the built-in Kindle UI running it will draw a menubar on the screen when the Wi-Fi connection status changes and power consumption will be a bit higher with this setup. All in all still a good tradeoff if you want to keep using the Kindle for it's original purpose too.

Edit: someone else posted a link to this tool which does exactly this: https://www.mobileread.com/forums/showthread.php?t=236104