It's doable in an ugly way, but to do it the right way takes a bit more effort.

To do it the ugly way, you just have to add the following line:

$msg = new Mail::Send Subject => $subject, To => $CPAN_testers;
$msg->add('From', 'me@example.com'); # add this line
[download]

This is at line 244 of cpantest (at least for version 0.034).

To do it the right way, you would have to store the email address in the CPANPLUS config hash, possibly using the installation's Config.pm $Config{perladmin} as a starting point, and patching the Makefile.PL to prompt for this as well. Easy to do, just need to find the time to do it I guess.

print@_{sort keys %_},$/if%_=split//,'= & *a?b:e\f/h^h!j+n,o@o;r$s-t%t#u'