I crank my monitors and put the singer in front of them holding an SM7. If they can't get into it like that, you'll never get a good performance. I manually cut all the bleed that comes from the monitors then go from there - tune, compress, filtering, further EQ if needed then delays into reverbs. I got the idea from Andy. Also saw Hetfield giving it some in the same style on Some Kind of Monster or some other St. Anger studio blog.
If you get the vibe right, you'll get the killer take. I've stood in an isolated vocal booth and it can be intimidating. You see a 2 grand+ mic in front of you and you think 'fuck'. Put a 58 in the singers hand with their music cranked to fuck and the hairs on their neck will stand up and they'll get goosebumps. That will beat the epic LDC hands down in my opinion. My opinion...