When Kane's out we change our formation, we play a false 9 where Son and Alli share the striking duties but also keep to their AM roles.
Hit ten goals in three games while Kane was out last season, inlclduing beating Chelsea away (which Kane returned in - after we'd hit the three goals).
Season before we beat Man City, Middlesbrough, Burnley and one or two others when Kane was out as well. Think Son his about 4 goals in that period.
Back up strikers just don't seem to work for us as they can't seem to emulate the way Kane plays in any way. That's why our AMs step up as they already know the system and what to do. If we're to use an actual back up striker, our best bet is to probably throw Kazaiah Sterling in, our young academy striker.