Nice MOD. I did the same thing back in 2007 on my Dell XPS M1710. I don't have a Dell Mini but the idea is the same. I didn't do it with the PCIe slot, but I did it that way on my new Precision M6500.
I am curious, where did you pull +5V power from?
You can read about my MOD
here. I used a mini PCIe to SATA/USB card. Follow the link in the first post to read about the M1710 job.
On the M6500, I pulled +5V from a fan, which had +5V all the time. It worked fine. A week later the system stopped turning on for some reason. I don't think the MOD is the culprit, but who knows. It worked for a week. Anyways, is there a better place to pull +5V from? I chose the fan and the card adapter so I didn't have to MOD the motherboard directly.