You could hypothetically use all that precast gear by making three macros to set all those slots with /equip, then cast the spell, and then use /equipset for your midcast gear, but... yeah, it's cumbersome. I guess the intended approach is to just always wear your precast gear rather than only wear it just before you cast a spell?

This is one of those cases where things would work a lot better if we could have /equipset without the 1 second lockout, but apparently that's not possible. 20 line macros would be good enough, but that would conflict with one of those PS2 limitations aspects of design so... not likely to get that either.