This example was done with BIRT 2.5 but should work with 2.3. It only uses one script on the chart.
function beforeDrawSeries( series, seriesRenderer, context )
{
if( series.getSeriesIdentifier() == "Series 1" ){
var dpharray = seriesRenderer.getSeriesRenderingHints().getDataPoints();
for( j=0;j<dpharray.length;j++){
var xval = dpharray[j].getLocation().getX();
dpharray[j].getLocation().setX(xval-30);
}
}
}
<br />
Make sure to name your series (third tab in the chart wizard).