This doesn't answer your question about types/access to the nuts, but I recently had to mend my heatshield for exactly the same reason. I did it with...the lid off a Pataks curry paste jar, put a hole through then seated the bolt on a large washer and passed it through the lid. I did this in 3 places; the nice thing about it (apart from being a free and long lasting fix) is that you can punch the hole through the jar off-centre if space is a little tight (you'll see what I mean when you try it).
Actually, I also sheared a bolt, but there was sufficient spreading of load from my 3 jar lids that I didn't need it anyway. Plus the purple lids matched the powerflex bushes ;-)...proper custom touch.
Although, I am fully expecting Ned & Co to take the micky when it goes up on the ramps at Autolusso later in the year.