Forgot to order block heater!!!!!!

I ordered this truck about 3 weeks ago, and I just realized today there is not a engine block heater listed on my invoice, my dealership today just gave me the serial number for my truck and said it would be delivered on June 20th.

IS it too late to change this order?????? OR if i can not change it how difficult would it be to install one?

If anyone can help i would appreciate it!

Serial Number# 1FTWW31P16EA31839 /ubbthreads/images/graemlins/shrug.gif