So essentially this would mean that in addition to the CSU endorsement, by minimum, there would need to be 3 Nav's flown at a Commercial standard?
Yes, if the school is doing things correctly. You can download the day VFR syllabus (or at least you used to be able to) and it will list all of the items of competency that you must demonstrate for a CPL test recommendation.
What you might be able to do however is simply talk to the school about doing all of your flying in this aircraft assuming it is insured for flight training and the owner is happy to let the school use it (even if only for you); or at the very least you could ask the CFI to approve you to do some of your solo navs in the aircraft and stay on the 150hr course.
P.S: It is my experience that very few students get through in 150hrs even on a supervised course, and of those the only ones were the students who could commit at least 5 days a week to flying training. Your typical CPL will take around 170-200hrs total.
If you can do this and save some money, are you going to spend it on quality CPL theory training?