Hey Bal, how are things? Here's the low-down on your issue.
This was a hot topic around a year ago, and those that remember it involved locating the points where the plugs were missing. Now, one of the people that attempted said it didn't work and upon closer inspection said there were resistors missing also. Someone with an XPS Gen2 or m170 would need to locate these resistors and identify them so proper equipment could be obtained.
The person that did get LED's working inside their machine ran them off of one of their rear USB ports for Power and Control.
And I remember pulling mine apart back then to help locate stuff, those soldering points are rediculously small. I would find it hard for even the steadiest hand to do it alone. A super-fine tip and some type of guide plate would be needed to get it just right if you plan to convert the motherboard.
As for the BIOS, you'll notice that the Dell Recovery/Diagnostics console in the 9300/Gen2/m170 doesn't have a diagnostic that checks response from the LED's, it just flashes them in different colors and asked if you saw it. This would lead me to assume that the LED controls in the BIOS are not self-sensing.