I have used...
BMX footpegs for my risers,
a VCR lid for an underseat cover,
a FF hemet facemask for a flyscreen,
a luggage lock for a tripmeter,
a hockey puck for a kickstand foot,
bicycle pedals for footpegs,
a drawer handle for a tailbag mount,
and a street sign for a license plate mount...
... but this guy takes the cake...

...
... bet they work good though...

...

... any other examples of repurposing?...