My version of ldapsearch doesn't have the -j option, however I see it does have a -y file option which I suppose will do something very similar.

However, since then ps -ef would show the name of the file where you stored the password, it should be made readable only by root or by the user running the openVPN script.

-j file read bind passwd (for simple authentication)
-w passwd bind passwd (for simple authentication)

So no need to obfuscate anything and a simple :

ps -ef

don'l let people sharing with you the server discover your password