Thanks to Marek [Atlassian]
it's possible to have extra coverage metrics in the HTML report. You have to use clover-report task and declare the current , columns element in it, as shown below.
<clover-report>
<current outfile="report/html">
<format type="html"/>
<columns>
<coveredMethods format="%"/>
<coveredStatements format="%"/>
<coveredBranches format="%"/>
<coveredElements format="bar"/>
</columns>
</current>
</clover-report>