Zenosboy,
Have you tried using Snapping Points? Snapping points allow you to "snap" an object to another, so that if the first object's height changes, the snapped object will move up and down.
You could use either a data selection or a text box with the "Dynamic Height" option enabled, to select your variable data, and set them to skip empty regions. Then, create a picture object with your signature. On the data selection/text object, go to it's "Snapping Points" property, and check "Set Snapping Point" to put a snapping point on this object. Usually, you put it on the bottom-left corner. Then, go to the "Snapping Points" property of the signature, and choose "Snap to previous object" to snap it to the data selection/text object. With this, you should be able to snap the signature, and have it move up and down depending on the amount of data.
NOTE: Do not try to snap the signature to a group. Even if a group appears to vary in height, it is not actually the case, it's height value never changes, and the snapping will not work.
For more information on Snapping Points, check out the documentation:
http://help.objectiflune.com/en/planetpress-design-user-guide/Default_CSH.html#/1504.htmlHope that helps!
Regards,
Raphaël Lalonde Lefebvre