Let me get this straight. You have a script that has the password in it unencrypted where anyone can read it, and you are worried that they will get a glimpse of it with ps. I think you need to figure a different way.
Since you are running the script on the server where DB2 resides, it may be possible to not use a password at all. I do not know AIX, but this works on linux. Just make sure that the DB2 environment is set up for the user.
Basically there may not be any feasible solution as long as you set permission to 777. Only thing seems possible not to use any password. The job runs local, you do not have to provide a password as Andy said.
However if you are able to set permissions to 700, which should be possible in most cases, .psec file method is most appropriate to connect to databases, even on remote server.
As long as you are on trusted domain, db2 should not require any password.