Echo sounding voices
 

I recently shot a short film on my XL2 ,but because of a family emergency my boom operater had to leave at the start of the shoot.To avoid abandoning the filming I mounted the shotgun mike directly onto the camera and continued.Most of the sound came out fine ,but a couple of scenes,especialy one shot inside a vehicle sound very hollow and have a slight echo effect.I used a Audio Tecnic AT897 shot gun mic directly into the camera XLR.
What I would like to know is if any of you guys know a simple way to get rid of the echo and make the person's voice sound warmer and more natural?
I have just started using Premier pro 1.5 editing suite so my experiance is limited to the basic's at this point in time.