There is a process called "remoting" that will allow your code to start and control a session of NX. However, this process requires compiled code, not a plain journal, so it may require an author license. There is an example of remoting that ships with NX (check out the example code in the NX install directory).
Alterantively, NX ships with some command line utilities that can import native parts to teamcenter (check the teamcenter integration -> utilities section in your NX help docs), which can be started from a journal. It should be possible to load up your assembly in native NX, query or modify the assembly, and start the command line utility with the necessary information to import the parts to teamcenter (no second session of NX necessary).