Seems pretty simple, I would use a mortscript for the device side since I cannot code. Set up a cron job shell script on your server (as long as its *nix, why wouldnt it be? its a server.. lol
) that listens for the client requests and then when it receives, checks if there is an update available and if there is, the client downloads in the background to the SD with the SD RUU utility. When it is done, it prompts the user if they want to install the update.
I have dreamhost and it supports cron jobs via web interface. It also supports SSH so shell scripting is no big deal, just point the web interfaces cron utility at the script
