I think this is possible, but it should always be a team server project. If it isn't already a team server project, you can upload your project to a new repository. Then you will have the run in sandbox mode available.
There is another thing you need to actually be able to deploy your app to the sandbox and that is the app cloud services module. Then it should work.
I think first you need to open your project in developer portal then click on Edit in Modeler. May be then from your modeler, click on Open App and select your project from Team server. May be then Run in Sandbox will be enabled. Because when we select an application from disk then this Run in sandbox is disabled. I hope this would help you.