I managed to replace mine without removing the bumper. Not sure if it was easier though.
Easiest way to remove the old ones is to break off the top part and push them down through the bumper.
The passenger side one is relatively easy to get at and can be replaced without removing anything. You have to go at it somewhat blindly...
The driver's side was nasty. I had to remove front driver's side wheel and washer reservoir in the well to get at it and still had a difficult time.
Ended up putting about 2 hours into replacing them. Not sure how long it takes going the route of removing the bumper.
Link to when I did the project on mine with a few pics:
http://forums.pelicanparts.com/showthread.php?threadid=101261
Good luck.
Gordo