Hi,
It's common to put 4 to 6 buttons on one Analog input. 8 feet should not be a problem if you run the data and ground as a twisted pair. Or use shielded twisted pair wire with shield ground, +5 and signal in the pair.
You could also use CAT5 ethernet cable which has 4 twisted pairs of wires. one pair as +5 and Ground, and 3 pairs as signal and ground easily gives you 15 buttons using THESE little keypads. Some example with code HERE (Code Updated: Better debouncing)
Or extend a PS/2 type keyboard and have LOTS of buttons...
DISCLAIMER: Mentioned stuff from my own shop...