Forwarding can only be accomplished by logging into the account and setting up the forwarding address in the mail settings. Then it takes the relay of a confirmation code through the receiving email which will need to be used to activate the forwarding.
Typically, its a best practice to keep work and personal email separate. If the "real" email addresses you are forwarding to are also work email addresses, you should seriously consider making the Google Apps account their "real" account. Otherwise the employee is going to be seriously missing out on a lot.
Migrate users with IMAP or POP and show them that mail is only one part of Google Apps.
Besides being able to use Chat, Calendar, Tasks, Phone Calls, Documents, Spreadsheets, Presentations, Forms, Drawings, File Storage, and Sites, there are 60+ services that they can access and use with their Google Apps account.
Update from comments: In the case of volunteers:
If the volounteer already has a gmail account, just have them use that. You can share anything you want with them as if they had an apps account. No forwarding needed.
If they Don't have a google account, they can create one with any email. This will allow them to just use their regular email address and password to access anything you share with their email address.
This can be done here:
https://accounts.google.com/NewA...So,
John@yahoo.com can sign up for a google account linked to his yahoo email.
The cons of this are that he will not be able to use services like tasks, chat, or gmail of course.
But you can share calendars and docs and sites with their "real" email. No forwarding needed.