PaddySaab,
This is of course possible though you will be doubling your work, effectively doing the same job twice. The main problem will be the condition of the bleed nipples. My experience is that they will be well rusted up and either 'round off' or snap at the first application of effort. ( Unless of course you have been a good chap and replaced them at regular , say 5 years, intervals ).
Once they snap off then get a 'Dremmel' or similar and carefully cut them off flush. Now start to drill them out VERY carefully so as not to damage either the threads of the bottom of the drilling where the nipple seals. When you get, using progressively larger drills, to the position that you are 'breaking through' the threads, then pick out the spiral of thread left and then run a plug tap down to clean out any corrosion, swarf etc.
If you don't fancy this then it is possible to do the job without using a bleed nipple. Take the piston fully out, clean everything in sight then completely fill the aperture with fresh fluid. Carefully re-engage the piston, expelling air through the hose entry. Do not push the piston 'home'. Release the clamp on the brake hose and allow fluid the drip, by gravity, down from the reservoir. As you enter the hose into the threads, gently press the piston in a little more to ensure no trapped air. ( Hose conecton at the top ) Now screw the hose fully in before pressing the piston home to allow fitment of the pads. Fiddly but possible, I know, I was that boy !!
Paul @ Kippen.