Whilst doing some research on plugging up brake holes and allen head openings, I came across a helpful post by 11.4 (who's always helpful and a great resource on the forums - hat tipped to you) about using a chrome button head allen bolt to fit inside your brake hole and using a recessed end (like you find on brakes) to bring it all together.
I've been to a few hardware shops and was defeated by unruly looking coarse threads, and unfinished metal. Thus to the internets I turn and I'm going to venture a guess that if you have a scooter store or an automotive tricked out shop or a motorcycle shop you might be able to find these but otherwise, here ya go.
This is a page and list of metric bolts, plug caps and other assorted things with a nice chrome or high polish finish to fill up any unaesthetically pleasing brake holes or to help plug up any open allen holes. On the latter, it might not be a theft-proof solution by far but for $0.40 it might be worth it as a deterrent.
You want the plug caps for the allen bolt heads and if you're looking to fill in any brake holes, you're most likely looking for a chrome button head allen bolt that's a metric 6 size (M6) with the desired length of your choice (about an inch or less) to fit your reccessed allen fastener.