Right-click the panel between the icons you want on the left and the ones you want on the right,
select 'Add New Item',
then 'Separator or Spacing',
unmark 'Draw Separator' (unless you also want to add a vertical separator there)
and mark 'Expand'.
Then right-click the icon(s) you want on the right,
select 'Move' and drag them.
I found this by trial and error. Maybe there's an easier way.