Press Gang reduces naval cost by 50%
Grand Navy increases Naval force limit by 100%
Going above your naval force limit increases cost by up to w/e % you're over.
You'd first pick up Press Gang so the ship costs are 50%.
Get 5 loans so you get enough money up front, and spend them all on carrack.
After you cede your provinces, your forcelimit will drop to one, and since you already have 17 ships, your cost will be x17.
With 50% build queue refund, you'd sell back a couple ships, get stab back to 0, drop Press Gang, refund the rests of the ships. Making HUGE profit.
Then you switch your NI to Grand Navy, so your forcelimit is now 3, making your cost ~x6.
Spend them all on carracks again, drop GN, cost goes back to x17, with refund money you'd still be getting ~x8.5 vs ~x6, there's your profit for stab cost.
Ofc it's a little more complicated than that due to the cost scaling of the queue system, but you get the gist of it.
Once you're gov 9, the process is further hastened by Grand Navy + Press Gang, so you'd spend your earnings on gov 9 first.
It's doable, but just REALLY time consuming and mouse damaging.
You'd probably have to spend hours of nonstop clicking, so get a macro/program that does the left clicks for you.
In fact, it's so time consuming that it's difficult for your MP friends to not notice it.
The difficult part of this strategy is the fund and the fleet so your first transaction can bring a sizable return for the future abuse.