gasperinn:
@GoForSmoke, i don't realy understand how do you meen, do you maybe have any shematic picture or something like that?
Using SPI bus shift registers, it would connect like in the Daisy chain SPI configuration here:
Daisy chain SPI configuration
The 3 SPI slaves would be 3 8-bit parallel to serial shift registers. A sensor would hook to each input pin which is not shown in the wikipedia diagram. The registers read the digital state from the sensor and on command, copies those as bits. Then the bits are shifted out of the chips and read by the master in as fast as 1.5 microseconds.
The register has its own power line, some people power leds off them on external power.