I'm working on my CFI certificate. I'm aiming to get both the
CFI-Airplane and CFI-Glider and since the book work is pretty much the
same, I'm working on them in parallel. I haven't decided yet which
checkride to take first and would like to keep my options open.

Here is the problem: I'd like to get the writtens out of the way but
don't know which writtens to take. If I were to do the CFI-A first,
I'd take the FIA (Flight Instructor - Airplane) and AFG (Flight
Instructor - Glider - Added Rating) tests. If I do the CFI-G first,
that would be the FIG (Flight Instructor - Glider) and AFA (Flight
Instructor - Airplane - Added Rating) tests. (I've already taken the
FOI.)

One option might be to just take the FIA and FIG. Is that allowed? Can
I show up for an "added rating" checkride with the "initial rating"
version of the written? I checked the DPE handbook but it doesn't
seem cover this situation.

Thanks,
Boris