A wheelie is performed by pulling back on the
whilst accelerating, be careful to not lean too far back as your rider will fall off.
land the Wheelie after you have reached at least 500m
wheelie distance, this will be displayed above your rider as you are performing the wheelie.
The way i did this was to setup a Custom Match with the following settings:
City - New York
Route - Brooklyn Bridge Strait
I chose the Ducati 998
but you can pick which ever bike you are comfortable with.
Here's a video demonstration, it did take me a few tries.