Unfortonately there is nothing you can do short of upgrading to v7
http://www.cisco.com/en/US/products/hw/vpndevc/ps2030/products_data_sheet0900aecd80225ae1.html
"CLI Usability Enhancements
• Enhances the Cisco PIX Security Appliance CLI user experience by incorporating many popular Cisco IOS command-line services such as command completion, context-sensitive help, and aliasing"
