How can I prevent OpsWorks Deployment from defaulting to deploying to my Custom Layer?

I currently have a relatively simple OpsWorks MEAN stack configuration, consisting of two layers.

One layer is the Node.js App Server layer, and the other layer is a Custom MongoDB layer. (As a side note, I hope one day Amazon will provide a Mongo store for OpsWorks, but until then, I had to create my own custom layer.)

I really like the way everything works, with the exception that when I deploy my Applications as shown above, the Deployment defaults to deploying to my Custom MongoDB layer as well:

Other than remembering to uncheck the boxes just before I click 'Deploy', I can't seem to find any way to specify, in the Deployment, Application, Layer, or Stack configuration, that I don't ever want my Application deployed to my Custom layer.

That's possibly not a huge deal for my MongoDB layer specifically, but it doesn't seem to make sense to have the application code over there in general, and I can most certainly envision application-specific custom chef configuration that I definitely don't want applied to my DB layer.

Can anyone point me at a configuration option or other mechanism for excluding deployment to a custom OpsWorks layer?

Thanks!

-- Tim