Ideas for adding weight to the AA MPR?

[RFC]

I just received my MPR and have begun tinkering with it. I would like to add a little weight to it and wanted to get your suggestions. For example, are there already weights available that can be inserted into the internal rail? If not, what about a "hardware store fix," such as the right sized bolts, washers, and nuts, or other fasteners, that can be inserted along the length of the internal rail or at specific points for balance. It may be time for one of my creative trips to Ace. It always confuses the salepeople there when they ask what I'm looking for and I reply that I don't know.