Would probably be easier with regards to actually routing power to the end-use device, and depending on that device, to use a linear or LDO regulator in a device to pull the 3v3 from either a +12V or +5V source, like how 12 and 5 are attained in the PEB. But that just satisfies primary power supply issues; one still has to interface the logic signals and maybe even RS232 signals.
As an aside, there is/was a project for Arduino, and a fork for MSP430 and Stellaris/Tiva (Arm M4F) stuff, which presented a UI on the computer, with toggles and buttons, and allowed one to read analog-to-digital converters and set digital I/O, PWM, and digital-to-analog converters. Something like that with a simple scripting language to handle "processing" signals could be more than a token curiosity, no?