GtkScale GtkHScale with multiple sliders and values?

[v4r4n <console cowboy gmail com>]

I've been trying to figure out how to create a GtkHScale that would let the
user determine the beginning, middle, and/or end of a single data set.

Ideally the sliders could effect each other, but the overall size of the
scale wouldn't need to change.

I was thinking I could have a silder on the scale that represents the start,
one for the center, and one for the end, but I can't seem to find an aspect
of the api that would allow me to add another slider on a GtkScale widget.

Should I look for something similar within GIMP?  I know I've seen elements
of Photoshop with controls like the one I'm trying to describe, so I'm just
assuming it would be possible to implement such a tool with GTK.

Do I need to derive a custom widget from somewhere?  Where should I begin?

~Thanks