With the extra likelihood of fogging, I'd say you need mesh over glasses rather than lenses. A fencing type mask will fit over just about any specs. Like
this. The problem with them is that you cannot get anything in your mouth, like drinks and/or sweets, without tipping them up, which may well send marshals into paroxisms.
I'm planning on adding a hamster-cage-esque door over the mouth area of the one i have - i have a piece of mesh which has some automotive purpose, but it doesn't really matter what, so long as it will stop BB's, because it's not like anyone needs to see through that part. I did also think about just velcroing it on...