i highly advise against doing this, you will regret it. this is one reason why they work so well....you will be cutting vapor production/performance significantly if you do this.
but with that being said here is what zen advised if you wanted to do such a foolish thing....take a blunt nose needle that will fit in the hole, cut a small piece of it and glue it in place, instant tight draw cap.
i will say this again....you will regret doing this