Update: I built this out and it works great to power the Gertboard and my rpi model B.
Attached are the parts I used. I replaced the Gertboard 3002 ADC with a 3202 while I was at it, hence the reason it's on the list, but that's certainly optional. I'm not sure if it's the new power circuitry or the ADC upgrade since I did them both at the same time, but there is a lot less noise in my analog measurements now.
Make sure to select the proper part quantities based on the circuit design, plus any extras you might need in case your soldering skills aren't up to the task. An extra fine point soldering iron tip would come in handy as well. The tip of my 100w soldering station is about the size of one of those golf pencils, and that made things a bit more challenging.