How would this work though? Would Bozza just replace the site with a message, is my guess. But I'm not sure that is quite right, as it would feel no different to days when we've had essential maintenance, or the site has been moved to a new host, and the site has been down. That has happened before, and as such, we are all just doing something else. A bit like replacing a minutes silence with just locking the doors to the ground and not letting anyone in.
How about we have the site open, but we should all agree to post to just one single thread for that 24 hrs, and all we can post on that thread is a pledge. So, for 24 hrs, the website is open, but for those who want to be part of this, they just go to the "Sponsored Silence thread : 5th September 2015" and just post the amount they pledge. No comments, no discussion, just a respectful silence.
Or if we feel it's a bit crass to see what people have donated, then send your pledge to someone by PM (it can come to me if you want Bozza), and simply post "Pledge sent" on the thread to show that you've been on the site, marked shown your respect by not diving into thread discussions, and left silently.
I'm sorry but I don't understand this need to almost dictate to people how they should deal with this situation. It's almost like it's not how you feel you should grieve but how you should be seen to grieving by others. Leave everything as it is and let individuals decide how they will show their respect.