@krsrn
When you connect an android device to a pc via usb, you can tell it to allow access as a disk drive. If you can get your users to do this, then everything else could be done via your .NET app.
i.e.:
Detect usb device, check update required, copy files etc?
I know it's not seamless, but it should be simple for the user.
Edit more info: Apparently some devices allow auto mounting, and if your users phones don't, I have read that there are apps available to do it. May help.