Coy, if you believe in LRLs then you can easily believe that IR will detect buried treasure. In fact, you can believe durn near anything, and that thread pointed to by auferret is a perfect example of people wanting to believe it works, and doing everything they can to prop up those beliefs.
But I think you're on the right track, forget trying to modify a standard digital camera and continuously wondering whether the fact you never find treasure is because you did something wrong. Go whole-hog and buy the RazIR, then when you can't find treasure you'll know it's because IR doesn't work that way, and you'll have the benefit of being able to sell an otherwise useful device and get most of your money back.