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I'm thinking something like this:

• The item should be itemvalid_FIELDONLY so you can't use it in battle and have a new use_script itemuse_teachmove where the use_arg is the ID of the move.
• The new use script should first attempt to learn it with amp_learn_move_instantly, this function returns "false" if the monster already has a full movelist and if so you'll need to create a menu. You can copy this code from obj_battlecontrol's Step Event case 32 (but in the itemusescript the AMP ID will be argument0 and the move ID will be argument1 rather than "exp_monster" and "nm").
  
• Instead of using mev_monster_learnmove_spawnmenu directly, make a copy of it that, in turn, uses a copy of mev_monster_learnmove_confirm to confirm moves. This copy of the function doesn't destroy ALL parent_menu objects (we want the inventory menu and main menu to remain) but only the intermediate steps, and it also removes 1 copy of the TM (assuming you want them to be consumable and not reusable like in XY onwards). Likewise the copy of mev_monster_learnmove_cancel also lets the main and inventory menus remain.