According to the maximizer help, all of these weapontype keywords (club, knife, accordion and utensil) are already for mainhand only, but that does seem to interfere with the offhand equipment selection.
Ex: Maximizing for "club, equip thor's pliers" will ignore the pliers and result in a failed maximisation for not meeting that goal.
Similarly, maximizing for "club, weapon damage" causes it to suggest either the ginsu (+100% weapon damage, 2-handed sword, which is good since I have iron palms active), or brimstone bludgeon+slime-covered club if I force it into 1-handed weapons. Both times, it ignores brimstone bludgeon + stick knife, which outweighs either.
As for functionality: accordions can't be equipped in the offhand, but for utensils', knives' and clubs' skill interactions only mainhand counts.
As such, I'm not sure if a boolean modifier approach is the way to go here, since that might result in an outfit with the requested equipment in the offhand (or maybe on the disembodied hand), which would then fail to give you the skill interactions (and seal-clubbing prowess) you were probably looking for.