I'd also say no to the bar- you holding onto the bar means your liable to pull yourself along placing alot of strain on your arm socket joints and do no core work. I know this as I used to hold onto the bar. I felt silly doing so but noticed when I let go I was unable to hold myself upright as my core was so weak!
Practice going slower and not holding on- you will notice your heart rate climb as you require more muscle to workout. If you feel your going very slowly, up the gradient until your climbing. You shouldn't need the bar anymore then if you were walking at the same speed flat yet will burn even more calories. But be aware at the end of the day your looking for quality over quantity. If it means you going back a few steps to get things perfect before going faster with the same good posture then so be it. Youd posture can count for alot, not just in terms of helping you burn more calories when you workout but also for preventing injury.
Why so long on one machine though? do you not worry your body will become used to this and so will stop burning as much/become more efficient? It could be worth your while changing machine a few times rather then keeping to the same one. You will also be able to train more then your legs (and arm sockets!) this way. Are you able to find a gym instructor? they can help you try new things on the machines and the best way to use them.
But as far as holding onto the bar, no in so many ways. Sorry!