You can use the hive.server2.proxy.user property to do this. First, you will have to login as a super John:
kinit john -k -t john.keytab john@MY-REALM.COM
And then connect using the following connection string:
jdbc:hive2://myHost.myOrg.com:10000/default;principal=hive/_HOST@MY-REALM.COM;hive.server2.proxy.user=jimmy