show presentation progress at beginning of new section

[wells_br]

Hello,
I find it quite useful during long presentations, to show the point in
the overall outline, whenever I begin a new section or subsection.

For example, if the talk is structured like

1. Introduction
2. Theory
3. Experiments
3.1 One group of experiments
3.2 Another group of experiments
4. Results

and if I come to the beginning of section 2, I would like to show one
title slide with

1. Introduction
2. *** THEORY ***
3. Experiments
4. Results

in the left column and may some text in the right column. When I come
to section 3, it should show

1. Introduction
2. Theory
3. *** EXPERIMENTS ***
3.1 *** One group of experiments ***
3.2 *** Another group of experiments ***
4. Results

Everything without "***" should be greyed out.

Is it possible to show such an updated outline automatically by using
some title masters, templates or macros? Whoever I asked said that
they simply copied their overall outline to the beginning of each
section with small modifications. I'd prefer an automatic solution
because then I don't have to follow any changes across several of the
progress slides.

Thanks
B.W.