Stock Tank mod to fill up completely

I have a 2008 Cali and I'm wondering if anyone has put a vented cap on the tank, closed off the tank vent, and now fills the tank all the way up? Seems like there is another quart to be had above the recommended level, that's 16 more miles on my bike.

I thought I could mod the stock cap but I don't see how the lock barrel is removed. I thought I would just machine an aluminum plug with a vent nipple to replace it. I can remove everything but the barrel. I fiddled with the key, I pushed both ways on the barrel pretty hard. I see o-rings in the gap between the barrel and the plastic cap so it seems like it isn't molded in.. Anyway, I don't want to damage the cap.

I see Buster's has a BRP vented cap ($47) for the stock tank. Before I buy one ( I was hoping this would be a "free" mod) I wonder if anyone has figured out how to get the barrel out of the stock cap, and if anyone has figured out what the full capacity of the tank is.

BTW, I will probably put a larger tank on but I'm not going to do that for a while. For now a primus bottle and maybe extra range from the stock tank will have to do.

Does this help?
Keyless gas cap <-- linky

That is the post that got me started playing with the cap in the first place as I also don't like having to unlock the cap. Alas, it just shows how to take the bail parts out.