i've tried to build EL expression out of strings within the repeat control.

...

<xp:this.value>
     <![CDATA[#{javascript:
         return '#{docVG.Feat' + lnr + '}';
      }]]>
</xp:this.value>

.....

But:

The rendered checkboxes are 'Readonly' and not clickable :-(( 

It is not clear how to achieve the individual data binding for each checkbox.

The complete Control looks like this:

<ul>

<xp:repeat id="repeat1" rows="10" value="#{viewFPbx1}" repeatControls="false" var="col" indexVar="lnr" disableOutputTag="true">
    <xp:checkBox uncheckedValue="">
        <xp:this.text>
             <![CDATA[#{javascript:
             col.getColumnValue("Subject");
             }]]>
         </xp:this.text>
        <xp:this.value>
             <![CDATA[#{javascript:
             return '#{docVG.Feat' + lnr + '}';
             }]]>
         </xp:this.value>
        <xp:this.checkedValue>
             <![CDATA[#{javascript:
             col.getColumnValue("Alias");
             }]]>
         </xp:this.checkedValue>
         <xp:this.defaultChecked>
             <![CDATA[#{javascript:
             col.getColumnValue("initial");                                   
             }]]>
         </xp:this.defaultChecked>
    </xp:checkBox>
    </li>
</xp:repeat> 

</ul>           

Make sure they are set to Compute on Page Load, not Compute Dynamically.  Also the Repeat control must be checked to Create Controls at Page Creation.