One plot line, different thicknesses

[Declan Vogt <drv102(at)ohm.york.ac.uk>]

I want to plot a data line on a graph, and emphasize a range of the data
by thickening the line. I'm having problems because of how the symbols
are drawn and was wondering if anyone can help me.

1. Use of max and min leaves a gap in the line:
	f=findgen(20)
	plot, f, /nodata
	plot, f, max=10.1
	plot, f, min=10.1, thick=2

2. If I redraw the thick line over the thin line, I end up with symbol
clashes:
	f=findgen(20)
	plot, f, /nodata
	plot, f, linestyle=4
	plot, f, min=10.1, linestyle=4, thick=2
	
I'm trying to get a line that looks like one continuous line, without
gaps and definitely without line symbols changing along the length of
the line. 

(Oh yes, and I can't use colour)

Any hints?

Declan