That's an interesting one. Since you said no to the Actuonics option, maybe one of these?
Gear tracks mounted to booms, with gearmotors running the pinion gear. Possibly either individual escs, or 1 esc with many micro switches to sequence sections and limit travel
Jackscrew and acme nuts mounted to booms, coupled to gearmotors, controlled as above.
Continious-rotation Servo set up as winch drum, pulling line through complicated system of pulleys to extend. Springs or second cable bed on winch drum to retract sections? Possibly sequencing the sections by different retract spring rates on each section?
. Something like.
https://www.youtube.com/watch?v=yInMEfrQWwA
. Or.
http://sariel.pl/2008/12/mobile-at-crane-6x4x2/
Post up a build thread!