Is it possible to automatically determine font size to fit text to a given space?

[Daniel Pittman <daniel@rimspace.net>]

G'day. 

One of the things I (ab)use ConTeXt for is printing little text labels
to Avery stock.  This works quite well, and I was pleasantly surprised
how easy it was to get working with some hints from Hans in the archives
of this list.

The labels, over time, have varying lengths of text on them, and to get
that to fit on a single label sometimes requires that I vary the font
size to avoid the text spilling over outside the bounding box.

Is there any reasonable way that I could automate the process of
adjusting the font size so that I got the biggest possible size while
keeping the text fully fitted to the label?


I don't mind automating this outside of TeX/ConTeXt, by using a script
to try the font sizes and examine the TeX output for overflow messages,
but I don't know quite what to look for.  

Hints about that, or a native TeX method[1], would be very much
appreciated.  At the moment it is a relatively slow process of manual
trial and error.

Regards,
        Daniel

Footnotes: 
[1]  I don't care if it takes ten minutes to run, since this isn't a
     performance critical job.