Patch-Tag now writes the _darcs/prefs/email file for repositories with the owner’s email.
That means if you check out a public repo (without being a member with write access to shared) you can contribute patches back to the repo creator simply with the command
This assumes you have sendmail configured for sending email from the command line. But if you don’t, no problem, you can output to a file and send as attachment. Every repo has instructions that will hopefully make this easy for newbies, for example one of mine.
Thanks for the users who suggested implementing this feature, now that it’s there it seemed obvious all along.