I've had another idea. Get a rubber bung to fit the can, make two holes in it to seal in two lengths of PVC tubing. One length goes to the bottom of the can and up into the filling spout. The other length goes into the air at the top of the can. With the can on the ground, use an air pump on this tube to force the oil up the other tube into the filling spout. Alternatively with the can on the bonnet, a short blow into the short tube from your lungs should start syphonic action.