Can you explain better? Are you saying that you want to have something like a pointcut that checks the value of the variable of class1 before deciding if the mixin will apply to class 2?
If that's not what you are trying to say, maybe a piece of code (even if it doesn't compile with JBoss AOP) showing what you want to do would help a lot!
Anyway, what is the relationship of class1 and class2? We need someway of going from Class2 to Class1. It is ok if this requires using package protected methods and fields.