You could build the insert by yourself. Here is an example:
% - Define dummy data.
t = 0 : 0.1 : 10 ;
yModel = sin( t ) .* exp( -0.2*t ) ;
yData = yModel - 0.5 + rand( size( yModel )) ;
% - Create/init figure.
figure(1) ; clf ; hold on ; grid on ;
set( gcf, 'Color', 'White' ) ;
% - Build main plot/axes.
plot( t, yModel, 'b' )
plot( t, yData, 'rx', 'MarkerSize', 5, 'LineWidth', 2 ) ;
ylim( [min(yData), 1.8*max(yData)] ) ; % Create space for insert on top.
xlabel( '\theta [rad]' ) ;
% - Build new insert axes + plot.
axes( 'Position', [0.6,0.65,0.3,0.25] ) ;
yDiff = yData - yModel ;
plot( [t; t], [zeros(size(t)); yDiff], 'm.-', 'MarkerSize', 5 ) ;
