indikit, I doubt it would be possible on any MP4 player, you would need a custom built firmware and I have no idea how you would go about getting that.
The only thing I can think of that may do the trick is a Portable DVD player that you could set to autorun a custom made DVD or VCD
http://cgi.ebay.com/Coby-7-LCD-Wides...QQcmdZViewItem.
Or a digital picture frame with memory card like this:
http://cgi.ebay.com/TFT-7-Digital-Ph...QQcmdZViewItem