nice DAvid Blain did a similar trick involving a watch store.

you have to remember that this is still a Magic show and that there are accomplices, sets and gimmicks involved.

It was obvious that he used a transmorphing liquid-crystal. a special glass used by alien ships (found in Roswell).

hahahaha. seriously, one solution is that the ones holding the paper are accomplices (hence their calm reactions as opposed to the freaking out girl).

The glass slides up and down exposing and hiding the built-in hole. He needs the paper to hide the clean cut hole. just the speculation of the people on the net about Blaine's trick.. I guess it applies here as well.