How to display the Who field in external calendar clients?

[John Gaida]

1. The user Admin creates a calendar entry with a Who field where a user is specified (e.g. John).
2. The resulting calendar entry is "John: Vacation"
3. In an external calendar client (e.g. Outlook) the event will display the author of the event and the summary: "Admin; Vacation"
   Unfortunately the who field is missing

How to format the who field into the calendar entry string displayed in external calendar clients?