Yeah, but I don't think a coffee would make much of a difference in an average heart rate during a ride.
I could see it rising my rate after I get out of bed and read the paper, but that wouldn't be the same as riding to work. My rate would be higher later in the day than in the morning anyway with all that I'm doing.
The coming home commute certainly, seems at least (and maybe) more challenging as the morning commute, but my heart rate is much lower.