My steps:

Base CentOS 6.0 AMI.
> Install Java 7 via RPM as root.
> Save as custom AMI.
> Use new custom AMI for Jenkins slaves
> Set up EC2 plugin as reflected in the attachment image.
> Run a build, and get the following errors:

Building remotely on i-0326a672 in workspace workspace/FriendList
Installing tools/hudson.model.JDK/java7/jdk.sh

[java7] $ tar xvzf tools/hudson.model.JDK/java7/jdk.sh
tar (child): tools/hudson.model.JDK/java7/jdk.sh: Cannot open: No such file or directory
tar (child): Error is not recoverable: exiting now
tar: Child returned status 2
tar: Error is not recoverable: exiting now
ERROR: Failed to install JDK. Exit code=2
Archiving artifacts

Installing tools/hudson.model.JDK/java7/jdk.sh
[java7] $ tar xvzf tools/hudson.model.JDK/java7/jdk.sh
tar (child): tools/hudson.model.JDK/java7/jdk.sh: Cannot open: No such file or directory
tar (child): Error is not recoverable: exiting now
tar: Child returned status 2
tar: Error is not recoverable: exiting now

ERROR: Failed to archive artifacts: target/*.jar
hudson.AbortException: Failed to install JDK. Exit code=2
at hudson.tools.JDKInstaller.install(JDKInstaller.java:189)
at hudson.tools.JDKInstaller.performInstallation(JDKInstaller.java:132)
at hudson.tools.InstallerTranslator.getToolHome(InstallerTranslator.java:61)
at hudson.tools.ToolLocationNodeProperty.getToolHome(ToolLocationNodeProperty.java:107)
at hudson.tools.ToolInstallation.translateFor(ToolInstallation.java:203)
at hudson.model.JDK.forNode(JDK.java:122)
at hudson.model.AbstractProject.getEnvironment(AbstractProject.java:311)
at hudson.model.Run.getEnvironment(Run.java:1993)
at hudson.model.AbstractBuild.getEnvironment(AbstractBuild.java:936)
at hudson.maven.AbstractMavenBuild.getEnvironment(AbstractMavenBuild.java:59)
at hudson.maven.MavenModuleSetBuild.getEnvironment(MavenModuleSetBuild.java:154)
at hudson.tasks.ArtifactArchiver.perform(ArtifactArchiver.java:115)
at hudson.tasks.BuildStepMonitor$1.perform(BuildStepMonitor.java:19)
at hudson.model.AbstractBuild$AbstractBuildExecution.perform(AbstractBuild.java:810)
at hudson.model.AbstractBuild$AbstractBuildExecution.performAllBuildSteps(AbstractBuild.java:785)
at hudson.maven.MavenModuleSetBuild$MavenModuleSetBuildExecution.post2(MavenModuleSetBuild.java:946)
at hudson.model.AbstractBuild$AbstractBuildExecution.post(AbstractBuild.java:732)
at hudson.model.Run.execute(Run.java:1568)
at hudson.maven.MavenModuleSetBuild.run(MavenModuleSetBuild.java:477)
at hudson.model.ResourceController.execute(ResourceController.java:88)
at hudson.model.Executor.run(Executor.java:236)
Finished: FAILURE