Can you not weld something onto the snapped bolt then bash it, spray it, bash it some more and use a wrench... probably easier than drilling...
On my stilo its all self tappers other than two under front bumper and two under the subframe (where wishbones bolt in).
I know this isn't an option on mine. It wasn't me that snapped them, the previous had just tie wrapped the tray in place.....
It looks like on mine the bolts have simply seized / rusted in place and rather than try and do anything constructive about it they've decided to just snap them all off.
You can see when the heads have sheared off it's taken the first few threads with it, so when you look it it the top of the now snapped bolt sits a couple of mill into the captive nut, so you've nothing to get any purchase or access on.
Ultimately for mine I think it might mean I have to take out the entire captive nut, replace some metal and put in new riv-nuts / captive nuts or something.
If they are what I think they are they're also enclosed threaded tubes the bolts screw in to, so it's not like a normal nut and bolt you could squirt some juice on top of and work it through. So once it's seized in there the options for getting anything in there to unseize are limited.
It's worth applying some form of grease of Vaseline to the top of the bolt, at least for those three across the front, so you know you'll be able to get them out again in the future.
I will need to address mine though. I'm fairly sure my airbox have jumped free from it's mountings, again, and is dangling from the bottom of the car by it's plumbing. So I'm going to need something to keep it in.