If you want to do this while getting all trophies for Mega Man X in one run, don't get the gun upgrade from Flame Mammoth's stage. Instead, get the gun upgrade from Zero in the first Sigma level and then use the Spira Crush Buster on one of the boss re-fights in the second Sigma level.
It might also work on the spider boss in the first Sigma level but I haven't tried that so I can't be sure.