There is a limit in how much you can send at once. If there is an actual provable limit in the combined total you can send in multiple seperate transactions, then that logically would just be a variable on the sender's end- keeping the same information in multiple places is a waste and I can't see them having implemented any such limit that way.
Really though, if the button presses aggravate you that much, just set up a keyboard macro to run through each of the 8 slots and pressing enter the appropriate number of times. Then you can just press your macro and go get a drink. This isn't a problem most players have to deal with on a constant basis. (emphasis to dodge arguments about how many people have to do it how often)