Your task might be an issue. I don't know if it's even possible to configure this way.
There are some options, such as creating a wrapper factory that handles the user/password so that you don't have to pass around the password all over the code - at least. Spring has one prebuilt for that as well.
Other than that - consider migrate to SSL authentication instead and set the user on the channel through MCA - that might be easier to configure in JNDI.