'When I Don't Have Anything Interesting to Play, I just Play Fast' But then who wants to hear 64 bars full of 32nd-notes except the douche-bag blowing them from the stage.
If the bench vise is a little out of your price range, you can always go for a pack of thick rubberbands and wrap them a few times around your balls lol. Or there is the tried and true technique right before going on stage
In all seriousness tho, a lot of screamo singers cant do it for very long. It tends to damage and scar the vocal cords. Avenged Sevenfold is a good example of this, the lead singer used to scream until their two most recent CDs. He had damaged his vocal cords and couldnt do the screaming anymore. Just a word of caution in case you are asking because you want to sing in such a manner.
Have you looked up "Zen of Screaming" and "Zen of Screaming II"? The vocal instructor has worked with the dude from Lamb of God and that chick from Arch Enemy, and they've got some pipes.
I tried the rubber bands, but could only get that squeeling-like- a-pig tone, not the deep growling devil sounds I was after. The vice was promising, but really slows down mobility when jumping into the crowd. (Great name for a pedal though, "The Vice".) The "ball kick" produced some very believable tones, but the effect decays fairly quickly then I wanted to vomit.
I always thought that screamo was performed with effects, but I guess not! Seems these vocalists are "pureists" when it comes to their "devil's" tone. Definitely not my thing, but I am curious about the motivation to perform screamo and why its popular.