I cannot find a way to do it mannually but it seems to be possible via script. Try this (change to your own column names):
Graph Builder(
Variables( X( :Month ), Y( :MeanRainfall ), Y( :Rainfall, Position( 1 ) ) ),
Elements(
Bar(
X,
Y( 1 ),
Legend( 3 ),
Row order( 0 ),
Error Bars( "Standard Error" ),
Summary Statistic( "Mean" )
),
Line(
X,
Y( 2 ),
Legend( 3 ),
Row order( 0 ),
Error Bars( "Standard Error" ),
Summary Statistic( "Mean" )
)
)
);