I would not recommend up shifting without nipping the clutch unless you want to buy new trannys all the time. If your clutch and cable are serviced and working properly it's very easy to nip the clutch with one finger. When you get used to doing it through habit it will be very easy, effortless and natural for you. When you are up shipping without the clutch aren't you missing gears sometimes? If you are missing gears this will wear out the shifting dogs in your tranny. When these shifting dogs get rounded off the transmission sometimes will slip into a false neutral. If this starts to happen you have to get it fixed as it can be very dangerous slipping into a false neutral. An example; you could be hitting the takeoff part of a jump in third gear and hit a false neutral, oh my, you're in for big trouble with the huge endo.
You might even see the top pros shipping without the clutch on occasion but I really doubt it. Even if they did occasionally up shift without the clutch they can get away with it because their transmissions are different than yours. They have special mods done to the tranny that makes them stronger and more slippery
, more efficient. Not to mention they're taken apart every few races, inspected, serviced and ready to go again like new.
So again my advice is get used to using that clutch when you up shift. It's not so important when you downshift because there's not much force on the transmission in downshifting. But there is a lot of force on the transmission when you up shift, especially if you keep the power on and powershift.
You can see all the techniques in this DVD of Clutch Throttle and Shifting Techniques.
Order the DVD disc or "Stream" online and see free DVD previews.