I achieved this by adding a background to my reports like this, for example:
<background>
<band height="802" splitType="Stretch">
<rectangle>
<reportElement key="rectangle-2" x="0" y="76" width="535" height="726"/>
<graphicElement>
<pen lineWidth="0.5" lineStyle="Solid"/>
</graphicElement>
</rectangle>
</band>
</background>
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