Still not perfect, but the best I could do after lots and lots of attempts. There's a debug trigger to spawn all helicopters and makes Matt come out of the van, which is supposed to be unreachable. However, there's a tree and invisible walls you can use to jump high and far enough to trigger it. The rest is just getting Matt through without him stopping. Or at least that's the goal.
To make it happen I had to use a specially prepared account that did not have the "I've fallen - and I can't get up!" challenge and that upon completing it, I'd level up because there's nothing to revive you or break the fall. For this I played undercover on overkill 103 times and restarted as soon as the "set up the saw" objective was available (the limo landed 16 times on the roof, 18 times on the balcony and the other 69 times it landed in the staircase). I also got downed during one of these attempts, so additionally I completed the challenge for that. The limo landing in the staircase gives 1,666K and when it stays on the roof or falls on the balcony you only get 1,222K and 889K, respectively. This is still the fastest way to level up as it's just 45, 55 or 75 seconds.
The only mod used was one to skip the intro because finding the door when you can't see anything isn't easy and relies entirely on the luck that you spawn in the correct place. I've attempted over a period of around 24 hours in total and the intro would only add useless time to it as the game timer only starts when you can control your character (when the intro starts to fade away). This is necessary to hop onto the van and saving more time.
Credit goes to Wicket for mentioning the challenge as a way to level up and noticing that Matt comes out with this weird debug trigger.
![](https://s2.save4k.ru/pic/o-kE4sQpUpc/maxresdefault.jpg)