Agreed on this!
I used aviation snips to cut two slots, about two inches apart, horizontally, at the bolts. Don't be a ballerina, just get in there and cut that sucker any way you can.
This allows you to partially bend that part of the heat shield away (to be bent back later).
You don't need much access to get to the cat bolts, I found that they come off reasonably if these are factory.
I've seen a video (and a good tip) with a guy that uses a drill bit to drill out the broken studs, just enough to put in small self tapping screws that will hold the shield in place.
@ 1:09:40 of the video
https://www.youtube.com/watch?v=83992gWhIsk