The solution for this is the same as in F1 2017
and is quite easy:
The The 1% club achievement in F1 2017 worth 81 pointsWin a 25% + distance race against 'Ultimate' AI opponents
Head to Grand Prix and select the following:
> Track: Monza
> Weather: Clear
> Race Length: 25%
> Rules and Flags: Off
> AI Difficulty: 101 to 110 (Ultimate)
If using Modern F1 Cars select a Mercedes and you'll start near the front. Any car will do however.
Use whatever Assists you like and have Flashback enabled just incase something goes wrong.
The above event setup will let you cut corners without getting penalised, the most obvious benefit being the first chicane. AI drivers will still take the normal racing line which means you will gain several seconds a lap on them every time.
A 25% race with these settings will take you about 15 minutes to complete.