Find the heat source..
Get a dual-use thermal camera.
Become the louis rossmann of the N900 community!
https://www.youtube.com/watch?v=FLSO0D67lOA#t=01m45s

If you get one you can help check where Leste is loosing the 80ma of sleep/idle current. [So it is dual-use technology. Because it has to be split your framerate will be low.]

(your finger tip might work as well, propably not for 80ma)