It is possible to iterate on a selection via the .subset. option, but NOT over the list of named atoms produced by COOR DIST with a double selection.
However, you can divert the list to a file via OUTU, process the list externally via the SYSTEM command which calls a script or program that produces a CHARMM stream file, then read the stream file. The script or program can use whatever tool you feel comfortable with, e.g. python, perl, bash script using awk and sed, etc. The CHARMM framework would be something like
open unit 2 write card name cyslist.txt
coor dist sele atom * cys sg end sele atom * cys sg end cut 2.5
system "makestr.sh cyslist"
Here, makestr.sh would process cyslist.txt to produce the patch commands required in cyslist.str. I've used a similar approach recently to generate a stream file to define a list of time series via the ENTER command of CORREL.