It's always struck me as odd that no one has ever made a brush handle with a lanyard hole drilled in it. That would allow you to run a piece of cord through it and hang it on the towel rack. It would be perfect for a travel brush.
A small drill bit, say 1/8" and monofilament fishing line should work well. Probably wouldn't be very pretty but practical. You could take the mono out when home or didn't need it. There is a seller on eBay that puts a small magnet in the handle of his brushes for hanging from something magnetic. I saw another brush that had a hook on the handle for hanging. Would probably want to use a $10 chinese brush or something cheap as it would probably ruin the re-sale value.