by taking the back off the JP cart and replacing it with a random US back
This is the method I used to play my JP 1.0 cart, and dare I say, the best solution to this problem.
What I did was first buy a screwdriver on eBay for $3-$5 dollars. To find one for yourself, just search eBay for "nintendo 64 screwdriver". (The 3.8mm is for the game cartridges and the 4.5mm is for the console. Obviously, you will want the 3.8mm.)
Then, once I had the screwdriver, it takes roughly 2-3 mins to screw on the new cartridge "back".
Easy!