I finally find out a solution for my problem:
I did the following:
A.jar // jar containing beans,
lib/A-client.jar // jar containing interfaces only
// containing references to A.jar as ejb module, lib/A-client.jar as java module
The deployment description of A.jar (ejb-jar.xml) must contain a tag <ejb-client-jar> referencing the client jar and this jar must be specified in the Class-Path entry of the MANIFEST.MF.
The client jar might be used in other ear files by doing the same trick.
The ear file is redeployable.