I think the only way to achieve this is to bind the tooltip to a div or tr in wich the button is displayed.

Put a div around the button if necessary and set style padding.

I'm using the div although at first I didn't see any padding in the properties but made it successful by setting the style property with value padding:4px. Some weird downside though is that the tooltip will remain there forever if I hover in and out the button too fast and the only workaround is to hover again slowly over the button to make the tooltip disappear. Anyway it's better than nothing. Thanks again!

I found another workaroun or solution, however.

I create a cc:

<?xml version="1.0" encoding="UTF-8"?>
<xp:view xmlns:xp="http://www.ibm.com/xsp/core" dojoParseOnLoad="true"
    dojoTheme="true">
    <xp:this.resources>
        <xp:dojoModule name="dijit.Tooltip"></xp:dojoModule>
    </xp:this.resources>
    <xp:eventHandler event="onClientLoad" submit="false">
        <xp:this.script><![CDATA[var ID = "#{javascript:compositeData.ElementID}";
el = document.getElementById(ID);
var Pos = findPos(el);
var div = document.getElementById("#{id:buttonDiv}");
div.style.left = Pos[0] + "px";
div.style.top = Pos[1] + "px";
div.style.height = el.offsetHeight + "px";
div.style.width = el.offsetWidth + "px";

function findPos(obj) {
    if (!obj)
        return;
    var curLeft = curTop = 0;
    if (obj.offsetParent){
        do {
            curLeft += obj.offsetLeft;
            curTop += obj.offsetTop;
            } while (obj = obj.offsetParent);
    }
    return [curLeft,curTop];
}
]]></xp:this.script>
    </xp:eventHandler>
    <div id="buttonDiv"
        style="position:absolute;Z-index:2;opacity:0.5;filter:alpha(opacity=50);background-color: #FFFFFF;">
    </div>

    <div dojoType="dijit.Tooltip" connectId="#{id:buttonDiv}"
        showDelay="1" position="below">
        <div
            style="font-weight:bold;font-family:Verdana;width:200px;background-color:lightblue;font-size: 12px;">
            <xp:label
                style="font-family:Arial Baltic,serif;font-size:16pt;color:rgb(255,0,0)">
                <xp:this.value><![CDATA[#{javascript:'BlaBBBB'+ 'www'}]]></xp:this.value>
            </xp:label>
        </div>
    </div>

</xp:view>
 

Now you import this cc into your Xpage and fill the compositeData with the Id-name of that button which should work together with the tooltip.

The cc reads the coordinates of the button and positioned the tooltip over the button.

There´s no need to disable the button. It couldn´t be clicked because the div is overlaing the button and.. you can leave the tooltip as fast as you can do it.