How could you increase the kinetic energy of a truck without increasing its velocity?

Kinetic energy consists of 2 elements, mass and speed. If its velocity, that is speed, remains the same, you have to increase the mass to increase its kinetic energy without affecting velocity.

Kinetic energy of something depends on its mass and speed. 
So if you want to keep the same speed but increase its kinetic
energy, then the simple answer is that you have to increase the mass.

But it's not as simple as that.

If there's a truck cruising along the highway, and you want to increase
its kinetic energy without changing the speed, then it's true ... you'll
have to increase the mass.  You might have a helicopter swoop in low
over the truck and drop some bales of hay onto it.  That will certainly
increase the mass. But that DOESN't magically increase the kinetic
energy.  More energy has to COME from somewhere.

When the bales hit the bed of the truck and the mass suddenly increases,
if the driver doesn't want his speed to drop, he has to mash the gas pedal
a little farther, run the engine a little faster, and let the engine deliver more
energy.  THAT's where the extra kinetic energy comes from ... extracting
more chemical energy out of more gasoline.