There is no example code to use PTP to take the picture. It is theoretically possible, but you would need to add a PTP client Android library to your plug-in. The camera USB API (PTP) is not accessible from the base SDK. I did a web search for a suitable library, but could not find one easily.
Koen Hufkens is using a THETA S with PTP to study changes to leaf colors. Information on his project is here.
I will relay your question to a guy I know at Ricoh. Can you explain why the dual-fisheye is better than an equirectangular image in your application?