[Moo] Tips: offset controlled by element.height

[campari]

Is it possible to set offset.y according to the heigt of current
tooltip?
I want to position the tooltip above the links. The content varied so
the heigt of the tooltip is different each time.

var oTips = new Tips($$('.sb_tooltip'), {
        className: 'sb_tooltip',
        fixed: true,
        offset: {'x': -20, 'y': DYNAMIC_OFFSET(?)}
});

Thanks in advance