JKS keystores can't be used without a password. The best option is to pass your keystore password on the command line somehow - for example, instead of using the ADT to sign your files, trigger an ant
build like in this answer.
If you really want to have a passwordless keystore your only option is to write your own implementation of KeyStore
(although you still have to be able to tell your signing tools to use it) - see the Oracle documentation for more details.