I stripped the stock one on my B12 a few years ago. I was able to remove it with a ball end hex wrenches. Then I replaced the bolt with a stronger one.

One thing to try is the proper sized hex wrench and a thick flat rubber band on top to try and get it to fill gaps of the stripped head with the hex head. Since it is a low pressure bolt it just might be enough to break it loose.

Stock was 2025 aluminum which is way too soft and (imo) a stupid place to save weight on one tiny bolt. Got a stainless steel version instead from McMaster Carr (have 24 spares actually as the one I was looking for only came in a 25 pack).