I was just wondering about this myself (though my bellows seems fine, I'm re-foaming this week and will be using the RB for a big personal project soon). The guy who sells bellows on eBay says he sends instructions upon purchase; you might see if he'll send it to you, tell him you need to see if you can do it before you buy.
You might also try John Goodman - he sells foam repair kits for the RB and his instructions are amazingly detailed. Very nice guy and he may know how to do it. JGood21967(at)aol(dot)com
The photos I've seen of the bellows show a plate with screw holes; I just set my shutter to T and flipped the mirror up - I can't see anything inside the body that seems right - mystified a bit myself.