This next hack uses weapon Ability Byte 0x80 to allow an item with a stat boost pointer to give those boosts even not equipped! Now you can have an actual Starsphere in your hack. Optionally, you can use a version that prevents multiple items from boosting the same stat; it’s included in the downloads. You can still have an equipped weapon + passive item boosting the same stat.
Note that Con and Move boosts are not part of this by default, due to the nature of the stat getters for these stats.
Download (FE8)