Ear clamps on the hoses are easy to fit & virtually impossible to remove ....pm me for more info.

After 6 months the OP has hopefully moved on...

you can proudly join the below

Here is the best. Take it as you will but his bike won't run after with out a heavy cost. It has to be done right so it's a small investment. Buy a small fuel container. Put it beside your bike with about 1 to 2 litters of fuel in it. Make sure you can not see through the container. after 3 to 4 days of leaving fuel in it. (might have to refill as its most likely been borrowed) Fill it with Methanol then top with gas for smell. Methanol will dry out every single hose / valve / rubber on his bike or car. This will seize the engine.

Enjoy

Yes another valve in the line would work. Or an electric 12V valve that only is open when the ignition is turned on.

Or just some hoseclamp around the hose.