I am not entirely sure... I kind of want to believe that no one has made a plugin as such so far...
What I suggest you to do is go onto the bukkit request plugins forum and post what you would like there.
Or post here in the Looking For section, but I think you'll have a better chance on the Bukkit forum. http://forums.bukkit.org/forums/plugin-requests.13/
Hello, I'm a very experienced plugin developer (over 2 years). You could edit there inventory by saving their inventory to a config when they log off and then assigning it back them when they come back. You could then make an inventory on your screen that replicates their inventory and you can put items into it, etc. Wouldn't be too hard to make.
The plugin openinv allows you to manually edit a players inventory while they are offline, so it must be possible, I just need a plugin that does it.
What I suggest you to do is go onto the bukkit request plugins forum and post what you would like there.
Or post here in the Looking For section, but I think you'll have a better chance on the Bukkit forum.
http://forums.bukkit.org/forums/plugin-requests.13/
~ Evan
It is, you'd have to give it to them the next time they're online though. Which is possible through the PlayerJoinEvent Handler in Bukkit.