Maybe...
Find the printer manual for that printer. Some printers have buttons you can
push that allow you to change settings. If that printer has such a setting, try
changing it to 20.
Sometimes, you can send a special printer command that changes that setting.
(Again, see the manual for the printer.)
Print to a .prn file (use the same printer as the user owns)--I don't mean a
text file that's created via File|SaveAs.
You maybe be able to build a text file with those control characters in it and
send both the Copies command and the .prn file to the printer using an old DOS
command.
copy /b copies20.txt + output.prn lpt1:
where copies20.txt is the file that holds that printer code and output.prn is
the file that you printed the data to.