First of all, thank you for the detailed description and screenshot!
This functionality is currently not possible.
By the way, your plugin looks really good. The recommended approach is to have a single entry point for your plugin and then to have separate items on the left which load different views on the right (as it is in your case). The SDK team is preparing a new sample plugin which will demonstrate exactly this.
We are planning to give plugin writers more freedom with regards to the object navigator, however, currently you cannot add a list of custom objects in the object navigator.
Thank you for the quick reply.
Please let me know where can i see the sample plugin for the recommended approach. Will it be available with the next update to html-client-sdk?.
Currently i am using html-client-sdk-184.108.40.20600-6311399.
Yes, the new sample will be available in the next vSphere release.