If you take the ''hydraulic-idea'' to a higher level maybe you can use a single sided swing arm of a sportsbike:
This is only a simple minded draw but you could mount the upper sprocket to the swing-arm
and even make some protection for it like a plate or something. The hydraulic tube can be
repleaced for flexible steel ones?! Just shooting some idea's...
But i think that it's gonna be a very heavy construction!
Good luck with you're build! I follow this thread!