I always find these kinds of techniques fascinating. Thank you!
At this point though I've used my own technique for so long that I keep using it even if there might be better ways to do it. I have a blank Excel spreadsheet saved that has each column and row expanded to make each field be 1 inch x 1 inch, with the margins set such that each page cuts off at 8"x10" (so left and right margins are set at 0.25", top and bottom at 0.5"). Then when I import a map image into Excel, I just pull the map image bigger and bigger until the squares of the map equal the size of each field of the spreadsheet, rendering each page 8 map squares by 10 map squares. Then it's just a simple print at full scale, some trimming of the sheets to remove the white margins on certain sides, then scotch taping the sheets together.
What is nice about this technique for me is that I can see right away in Print Preview how many pages the map is going to print at, and whether there are pages at the edges that are only one or two rows or columns-- which allows me to decide whether to bring the image back into Paint and crop the map down a bit so that I can end the map edges to mostly full sheets (thus saving time, trimming and tape.)