[Coco] Getting more out of floppy disks

[CoCo Mongrel]

So for the game I'm working on, I'd like to get as much out of a single
floppy disk as I can without wasting a lot of CPU or memory on complex
compression algorithms.  I would like to provide the option for those who
have more modern floppy drives or hard drives with multiple RS-DOS
partitions to use them to store lots of game data.

I have 80-track (3.5") drives on my CoCo, but they're being used as 35-track
double-sided drives.  I still prefer the 720K floppies, even though there's
a lot of waste (though I do use the full capacity in OS-9) because data
transfer with modern PCs is easier using 3.5" disks.

I know there are DOSes, and patches to stock RS-DOS that go from 35 to 40
tracks, and that allow you to map the second side of the disk to otherwise
unused drive numbers (e.g. 2,3).  But on 80 track drives, that still only
uses half of the disk.  My understanding is that BASIC's FAT buffer would
have to be expanded in order to use 80 tracks (or something like that).  But
how difficult would it be to make DECB treat track 40 as track 0?  That way
you could have a whole upper bank of 40 tracks on each side of a disk.  The
inconvenient part would be that you'd have to poke a bunch of changes back
and forth to switch between the lower bank and the upper bank, so it
wouldn't be well suited to everyday interactive use.  But it wouldn't be at
all difficult to make a BASIC program keep track of which bank you were in,
and just have a subroutine to patch DECB for the lower or the upper 40
tracks as necessary.  Or am I fooling myself about how difficult it would be
to get BASIC to add 40 to its tracks?  Any thoughts?

CoCoMongrel