I solved it like that:
I created a modal-dialog without "modal" container:
<div class="modal-dialog" id="popup_tool_mouseposition" data-backdrop="false" style="display: none;">
<div class="modal-content">
<div class="modal-header">
<button type="button" class="close" data-dismiss="modal">
<span>×</span>
</button>
<h4 class="modal-title" data-i18n="tool.mouseposition.title"></h4>
</div>
<div class="modal-body">HUHU</div>
<div class="modal-footer">
<button type="button" class="btn btn-default" data-dismiss="modal" data-i18n="com.close"></button>
</div>
</div>
</div>
and now i stylied it like that... very cruel at this moment... i'll fix that later
$("#popup_tool_mouseposition").show();
$("#popup_tool_mouseposition").draggable({
handle : ".modal-header"
});
$("#popup_tool_mouseposition").width(300);
$("#popup_tool_mouseposition").css('position', 'fixed');
$("#popup_tool_mouseposition").css('top', '0');
$("#popup_tool_mouseposition").css('left', '0');
draggable() comes from jqueryUI