How to add a Java instance as context when using clojure as a scripting language?

Question

I found the amazing question How can I use clojure as scripting language for a Java program? which helped tremendously, but I can't figure out how to get an existing Java instance into Clojure. The use case is something really similar to AutoCad's AutoLisp. I want to let users manipulate an application with scripting so that they are free to do more without my help or input. I want to have a class that does some work

public class Testing {
    public void work() {
        // ....
    }
}

and then add it to Clojure

public class Main {
    public static void main() {
        Testing t = new Testing()
        IFn eval = Clojure.var("clojure.core", "eval");
        System.out.println(eval.invoke(Clojure.read("(import Testing)")));
        // How do i get "t" into clojure?
        System.out.println(eval.invoke(Clojure.read("(.work t)")));
    }
}

However I can't figure out how. I don't seem to be able to invoke def with arguments from java. I have been fiddling with this and with documentation for a while and can't seem to figure it out.