I know this tread is a few weeks old, but I was looking around for info and saw it. I found the following formula based on heart rate which is what I think my heart monitor uses (at least similar - it does not figure differently male to female).
[h=3]Equations for Determination of Calorie Burn if VO2max is Unknown[/h]

• Male: ((-55.0969 + (0.6309 x HR) + (0.1988 x W) + (0.2017 x A))/4.184) x 60 x T
• Female: ((-20.4022 + (0.4472 x HR) - (0.1263 x W) + (0.074 x A))/4.184) x 60 x T

where

HR = Heart rate (in beats/minute)
W = Weight (in kilograms)
A = Age (in years)
T = Exercise duration time (in hours)