Easy, dont install any Nvidia driver.
Then go to device manager, search for the generic display adapter with a yellow warning triangle over it, right click, disable, done, its dead.
The 740m as some defect because I have seen hundreds of those GPU's dead, mostly in the K56CB, the most likely culprit is the crappy thin heatsink that clogs in a couple months, and people that NEVER clean their laptops, so, too much heat and it dies, reflowing them wont bring them to life in 80% of the cases, and when they come back, they work for a couple weeks and they are out again..
For an eGPU solution, it will end way more expensive than you think it will, it gets cheaper to just buy a new laptop or build a desktop than to sink 500€ to have a mediocre performance, and if you plan on using the internal display count on loosing around 20% of your already bad performance because 1x PCIe is just too cramped to pump all that data back and forth.