Radiant heat garage floor - retrofit??

[RussMurco]

Ok, after spending much of the holidays in the garage, with single-digit temps outside, it's just a little too cold for my taste out there! My garage is 5 years old, 35x40, completely finished and fully insulated with gas heat yet the floor and my tools remain cold even when the air temp is at 70 for days.
Is it possible to add another layer to the floor with built-in radiant heating, or will I have to pull-up the entire concrete floor and re-pour??