I wrote and released a very simple library to easily add additional 12-bit DAC lines to your Photon/Electron for instances where the 2-on-board ones won't do. The perks of this DAC include 9 possible i2c addresses (more info here) and an external reference voltage, so you can easily add support for 0-5 VDC or 0-10 VDC (common for instrumentation). The IC itself comes in a few packages that should easily fit on a generic breakout board (VSSOP-8).
If anyone has one and can give the library a try, it would be greatly appreciated! Additionally, if there is demand, I can draw up a custom breakout board and make those available some how.