It is currently not possible. What can help you, however, it to use the Timecode window and set the position display relative to the active clip start. When you do this, the edit cursor will give you the desired position.
This being said, I will add this requested feature in next (major) WaveLab version, that is, to have the info directly from the popup tip.
Yes, right now I do use the timecode window and change it to clip or track start. It would just be a nice little time saver and feature if the info was directly available in the pop up. Thanks for considering it!