The .pcf file is just a text document and it is designed to be edited just like any other INI file. It is hard to find the documentation on the format but here is a good starting point: http://www.cisco.com/en/US/docs/security/vpn_client/cisco_vpn_client/vpn_client500_501/administration/5vcA.pdf#page119
Specifically Chapter 5-1 Preconfiguring the VPN Client for Remote Users this is for vpn client version 5.0 but the format does not change a whole lot.
The nice thing is that not all the values have to be set, just the ones important to you, or that you want the user to interact with.
Here is the a sample from the pdf in case Cisco moves it:
Description=connection to TechPubs server
BackupServer=Engineering1, Engineering2, Engineering 3, Engineering4
As you can see there is a GroupPwd and an enc_GroupPwd field either one can be set and as what Evan Anderson mentioned, there are plenty of tools that will break the encoded fielded so it gains very little security if you are trying to keep this a secret from your users.
Save that in notepad with a .pcf extensions and your users can import it for you.
Though the quickest way to create a pcf file is just do a remote session to your first mobile users computer. Enter the information in the vpn client, and then email yourself the pcf file it created. The building it by hand method is really designed to turn on features not available through the gui.