http://www.chevytalk.org/fusionbb/fbbuploads/1385662673-rsz_pb190072.jpg

Here is the link to the pic on chevy talk. It looks like it is what you are saying, Tim...an expansion plug or something like that.

I guess I just need to pry it out and get the same size one from the local auto parts store...they said you can get the ones that screw in.