(imported comment written by Lee Wei)
You can use the UNIX switch user (su) command.
For example, for a per-command basis, it would be:
su user -c command
A example of an ActionScript (not tested)
delete __appendfile
appendfile #!/bin/sh
appendfile su leewei -c “/usr/bin/some_command”
delete "/tmp/runcommand.sh"
copy __appendfile “/tmp/runcommand.sh”
wait chmod +x "/tmp/runcommand.sh"
wait chown leewei "/tmp/runcommand.sh"
wait “/tmp/runcommand.sh”
Lee Wei