You simply have to delete the object from the Display Tree; Below is a simple example.
names default to here(1);
dt=open("$SAMPLE_DATA/big class.jmp");
biv = dt << Bivariate(
Y( :height ),
X( :weight ),
Fit Line( {Line Color( "Medium Dark Red" )} )
);
report(biv)[PictureBox(2)]<<delete;
Jim