Why would you want to? If you have a problem with something sort it out whilst onboard and then consider your options. My Time Dining is done on the understanding that you will pay your gratuities up front, if you don't want this to do this you will have to use the other dining options.. ....Neil.
Not if you want My Time dining. How on earth are you going to pay all the different staff who serve you?
Simple answer NO. The only reason most cruisers want to "pay as they go" is to get out of paying the tips completely.