Fifteen Game : preventing jumps across the board

I'm trying to make a Fifteen-like game (also known as Mystic Square and things like that).

The link for the project : http://dl.dropbox.com/u/1412774/fifteenGameNormal.capx. That one uses a linear presentation for the tiles. Here's one which needs the Random Array (at least the first version of the plugin...) : http://dl.dropbox.com/u/1412774/fifteenGameRandom.capx

I've recreated the simple barrel mechanism to switch together two values (here two tiles of the game). What's bothering me is that the player can make "jumps" across the board. I need a simple mechanism to prevent players to switch tiles that aren't nearby. Any idea ?

Edit : at the very moment I hit the "Post" button, I realised what's the solution.

So I updated the two files. They are know working as intended. Sorry everybody...

Now, I just need to find a quick & clever way to know when all the tiles are ordred in the right order...

If somebody has an idea...