It is actually quite easy to get into the pit lane, two of us have done it every year on Wednesday and Thursday night. The race is a bit harder though. But as said above, once you are in very few people even take a second look at your pass. The smaller 911 teams are always willing to let you browse the pit.
Last year some guy in the Panoz pit let us see during a pit stop.
You have to know where the secret pit entry gate is though first
SL