Then use a 7amp, I should think that even a .35-.5 wire should be ok for that current load & they're the smallest on the car.
He has a few options, he can take his pick, personally I create a new fuse position for anything that isnt spec'd for that position.
Also certain fuses are rated based on the combination of components, so eg. if fuse 4 was a combo of say pdc & interior lights, alot of cars dont have say the pdc but the fuse may still be rated for that circuit, if it is then I see no issues tapping into that position Halls, checking the car fuse guide helps.
As I said common sense prevails, well it should anyway & if he's doing this himself he must have a degree of technical knowledge to realise current loads & wire gauges, fuses etc.
Only certain way to know it wont be an issue, is to create a new fuse position from spare ones.