If that was possible, u could easily select faces in the 3d view and uvmap them to a trim sheet for example. Especially if the faces are many. If there was a script to do this that would be awesome :- )
Out of curiosity, could you explain why you want to do this? Step mode for edges already exists in the form of 'point-to-point seams', but drawing a blank on why you'd need to do the same for faces? It probably wouldn't take too long to script though.