My knowledge of this was theoretical before, but now I have actually done it, and it worked exactly as described in the wiki (cashier pressed K1 key between RB swipes). At the end, I swiped my CC once to pay the cumulative total of three "items", just as I would for a purchase of multiple physical items.

Now no one seems to know why I couldn't load $1000 in one swipe. $800+800+899 worked fine for me today---I stopped short of $2500 just in case at my store you have to load less than each limit rather than less-or-equal.