That's right, 2 and a half years after the game came out, we are still finding new things out. Thanks to the brains of me, Baldred and Diablo combined we figured out how to do it.
https://www.youtube.com/watch?v=mw-W_ckgw-M
1. Set your seat position to be all the way in height and position (furthest to the right)
2. Go into interior view. (obviously)
3. Push up and hold up on your right stick. (or whatever control option you have for looking around)
4. Hold onto RB (change view button) for a few seconds and wait till it locks the view by showing 5x icon.
5. Enjoy!
With some cars you won't want to hold the view all the way up before locking so just play around and see what suits you best! :D Adjust seating position to your preference afterwards also.
Note: The view will reset if you reset the car or jump to the outside views. The view will still be locked but it will be locked at default so will require steps 3 onwards again.