I've never tried it either. I (only) suspect it's a case that you'd have to assume the worst. Every time I've gone through coach hiring, there are invariably one or two owners who wait, do nothing, or are flat out absent and miss coach hiring. So unless you are certain that, say, all 32 BL coaches at a position are hired before the last cycle - and I don't know how because once you sign yours you stop seeing available openings - you'd risk the AI auto-signing a coach for you.
I only bothered to try to track it one season, but the one time I tried following who looked like they had coaches auto assigned, all the coaches I saw who got jobs were ones who had not worked at all the previous season. I can't confirm whether it was a coincidence, or whether that's actually a criteria for the AI to choose.