Need a gimmick

Jim said:

Riding for charity on some long rides next year, I want to raise some prior
sponsorship while stationary at shopping centres and Car boot sales etc.

I can set up the bike on rollers and pedal away as I have seen others do,
but is there something else I can do using the energy generated by the bike
to attract a bit more interest? Music, or spinning a tiny kids
merry-go-round are some ideas I have been given, I'm not that much of a
DIYer but I welcome any ideas. Thanks in advance

It shouldn't be that hard to stick a dynamo on and wire it up to an amp meter / light board.... That way you can charge per watt / amp.

oooohhhhh - here's an idea, set up a cycle computer with the pick up on the back wheel and you can see the speed / distance ticking over. Hold a competition for nearest guess to the end of day distance....