Weird. I'll look more to see if the split can be configured. I just got a new Mac and I'm wanting to make sure everything in my NTFS guide on Mac works properly still, anyway.
OK. I did my experiments using my new Mac and WiiJManager. Here's what I found.
When splitting a larger .ISO file, the .wbfs files is "4.29 gigs" and the .wbf1 file is whatever is left.
But Mac apparantely isn't converting true bytes into true gigs using 1024 as a multiplier. I think it's just using 1000 as a multiplier and being lazy.
The .wbfs file that was created was 4,294,934,528 bytes. Drill that down using 1024 as a multiplier to gigs and you get 3.99997 gigs.
So even though your Mac is reporting that it is 4.29 gigs, it truly is 3.999 gigs and will fit on a FAT32 partition.
But for some reason that made the game not play at all, and once I tested it using 3700M instead of 4G, thus creating a smaller wbfs file the files started playing.
That is a 3-year-old version of "wit" that WiiJManager uses. You could try to swap out with a newer version and see if that helps. But again, I've not my share of failed transfers using that tool as well. I prefer my Windows tools.