Why was denny even involved if the car was only to be paced?

the contest winner,hamlin and waltrip met at the track and waltrip said he was going to drive the car "instead of denny". why was denny involved, how could he drive the car on a pace lap anyway? why was he even there if the car was only supposed to be paced? i know i heard this on the broadcast. and to trust this to MWR was insane with little mickey driving.