What about hiring some ace people (isn't that what our recruitment processes always do?) and then what about letting them get on and do it??
I mean really, just trust them and let them get on and do it.
Don't fuss around, don't look over their shoulders, don't check their work (like you know better), don't pretend you want to help when really you are trying to criticise, don't do performance reviews, don't ask for milestone/interim/stage reports, don't arrange 1:1s to make you feel like you are busy.
Just tell 'em why they are there and let them get on with it!
OK, that's ridiculous...tell you what, you can ask them if they need help, you can ask them what you can do for them, you can ask them how you can make their job easier, you can ask them what needs sorting out and you can ask it often. But only if you make yourself useful and do something about it...otherwise butt out and let them get on with what they are there to do!