Hi guys.
I got the same problem and, in my case, there was no other way to open, but from inside. So, I highly recommend you, in case you have this as an intermittent issue, fix it before you are no longer able to open it. This will save you time and effort.
From inside, I've removed the hand grip and the carpet trims, but I was not able to remove the panel because of the latch. So, I folded it enough to expose the latch plug and not to cause any damage tot he panel.
Then, I got the 12v from the rear light. Before connecting, I used a power meter to make sure.
Here is a picture showing the latch plug indicating the pins to inject 12v and the ground. As soon as I injected 12v and grounded the second pin, it worked.
Notice that this image is from inside perspective:
Here is the cable after opening the trunk:
And here is the broken cable (It seems that this already happened in my car and someone installed a connector, which is now broken again).
You should get 12V from that wire:
I will solder the broken cable.
I think it's a bit short so I am going to add a new piece of cable to give more room when opening and closing the lid. Then, I will use a tape to protect it.
If I get the same issue in the future, I will by a new wiring.
As others have mentioned, before putting effort on opening it from inside, check the switch near to the registration plate (open button), from outside.
Cheers