How to place a comma in 'a{b,c,d}e' metanotation

[rouben at math9.math.umbc.edu]

The csh man page explains how the metanotation "a{b,c,d}e" expands into
"abe ace ade".  What it does not explain is how to place commas in the
output, if necessary.  For instance I wish that the construction
"a{b\,,c\,,d}" would expand to the comma separated list "ab, ac, ad",
but it actually expands to "ab a ac a ad".  I guess I do not know how
to escape the ',' character in these constructions.  Does anyone know how?

PS: This question came up when I wanted to extend the font path directory
of my X server.  The command I wanted to execute was:
	xset fp+ /path/dir1, /path/dir2, /path/dir3

so ideally I would have liked to say:

	xset fp+ /path/{dir1\,,dir2\,,dir3}

which does not work because the commas are not escaped correctly.
--
Rouben Rostamian                          Telephone: (301) 455-2458
Department of Mathematics and Statistics  e-mail:
University of Maryland Baltimore County   bitnet: rostamian at umbc.bitnet
Baltimore, MD 21228,  U.S.A.              internet: rouben at math9.math.umbc.edu