Thank you very, very much! Alas, I had to resort to basically formatting each email_address => names pair individually and joining them.

I had hoped that Perl6::Form would support my scenario, but now I have a solution that works. It is probably less efficient than it could be, but the number of records I have to deal with is low enough (a few hundred email addresses with about 2.5 people per address on average) that it does not really matter. The script takes a few seconds to run on my laptop, which is entirely acceptable given that this script will run about once a week.

Again, thank you very much for your help!