Sorry to add another gloomy note, but in order to add a twin-engine type rating to your PPL(H) you will need to have completed the CPL(H) ground exams or be certificated as having demonstrated knowledge to that level. The latter means that if you don't do the formal exams you would have to undertake an approved groundschool course to gain that proficiency level before starting your type rating course. There may be TRTOs out there who have this approval: but check first.
Sorry, this is off the top of my head: it's in LASORS.
It was, of course, much easier in the days before JAR-FCL came along....