The cleanest way is probably to build a native extension for WEH6.5 and implement the RAS functionality you need.
Another, q&d, way to achieve this could be to have a small C app that takes a command parameter to activate or deactivate a RAS connection.
You can then call this app from RhoMobile passing the relevant parameter. The RhoElements v2.2 generic API is probably the simplest way to achieve this (Launchprocess and companion methods).
Thanks for the inputs. We will check the way for the extension and get back to you.