I lost the flag on our Chariot at the beginning of this season. We still had the pole, so I tied and taped orange safety tape at varying heights of the pole. Not the prettiest thing on the road but at least it is visible. One of the complaints I got from another rider last year is that the flag was at the same height as my helmet (from her vantage point), making it very difficult to distinguish the flag.
I also use a LED on back of carrier to help drivers see us in low-level lighting.