Well, there's nothing in the RAM that would allow to get the moves in an easy way. There's a (quite complicated) board representation, but this would require to keep track of the current board position in the plugin, compare it with the new one and then build the move from the difference - nothing I'd like to do in LUA!
The other way would be to read all 4x7=28(!) single segments of the 4 digits and build the usual digit code for each from the 7 correct segments, again a lot of necessary LUA code in the plugin.

So I would have the 'choice between Pest and Cholera' (as we say in German), and I won't like to get any of them -
so I'll probably remove this Super System IV from the list of engines usable with Winboard/Arena.