I have a pair of that style lever that I'm using non-aero. I
think that the piece that goes in there for aero routing would keep the barrel from moving but I didn't have them so I came up with my own fix.
I purchased a piece of Kydex on eBay, cut out a strip the width of the opening and about 1.5 times the length of the slot. I heated it and folded both ends back over themselves; once I inserted it into the slot I then heated it a bit more and moved the folded parts back towards the ends to hold it in place. I did this a about 3 years ago and I haven't had any problems with it yet.
It's hard to get a pic of what I did but this should give you an idea.
