I use to run a rear airless green tire.
http://greentyre.com/bicycle-tyres.php
There is a knack to fitting them, I think they came with a pair of green paddles used to lever the tire on. Together with zip ties it is do-able you just need to trust the tire will give at the right moment.
I have to say the ride was harsher and at times skitich on wet slippery surfaces. I don't know if this is true for this version though.
I moved back to proper tubes when i got my new bike, then bought Schwalbe Marathon plus, with thick Raleigh TA411P Puncture Resistant Inner Tube. Bewarned short valves. To pump these you may need a locking nut for the valve, or a schrader valve extender. Finally i also topped up with green slim.
If you want to avoid the pain of completely removing your hub motor to fit a new inner, you might want to pop for the easy fit susage-like 'Gaadi Double End Inner Tube' as your spare.