With the transmission in neutral, it doesn't matter if the clutch is engaged or not. Also, if you jack up one rear wheel and put a jack stand under the axle housing, the wheel can spin as the engine turns and the truck won't move. When I'm working by myself and need to hold the clutch or brake pedal down for some reason, I cut a piece of broom stick or a 2 X 4 to length to wedge between the seat and the pedal.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!