There's a device called an Audicator, which sounds an audible alarm after x number of flashes, with the sound getting louder with time. It's intended for motorcyclists, who have the same problem. I got one for my last Roadster, but hadn't got around to fitting it. Come the summer, I see about fitting it to this Roadster...
I have one fitted to my 4seater...........best accessory I have ever purchased ( usual disclaimers - just satisfied user )

Neil.