There are hydraulically operated clutch systems available that presumably make the clutch operation lighter, but besides the slave cylinder grafted on to the side casing, there must be a hydraulic clutch lever on the headset end. My point is that somebody has done the 'engineering' that might benefit you.
However, there is a system available via:
http://mail.nabd.org.uk/adaptations/Adaptionkits/that is a hydraulic to cable clutch system.
I wondered whether that may be used in conjunction with one of the remote front brake hydraulic systems that some Lambretta owners hide behind the horn-casting, though I guess there would be some losses in efficiency compared to a 'pure' hydraulic system.....
I had a trawl of t'internet to see if there is a servo system available for bike clutches, as I'm sure the problem is not restricted to scooter riders. Perhaps a motorcycle Forum might yield a solution that you could apply.