To do an unlimited wheelie steal yourself a Sanchez (Dirtbike). Now lean back to do a wheelie. Now gently lean back to the normal 'drive' and Tommy will do an unlimited wheelie.
If you do it correctly the front wheel will be 'stuck in mid-air' and you can drive around at full speed all across the city.
Escobar international, from downtown to the harbor and ocean drive are the best places to do this, so you can turn without hitting anything. but if you want a challenge, try little haiti and little havana.
I once pulled a 10 minute wheelie.