vex, if lash not already a group on poser figure's head, it can be made a group using group editor.
create new group, rename new group, add material (e.g. upper or lower lash).
then mag zone for head can be restricted to lash group, whence mag will only affect said group.
unfortunately it tends to move the lash around a bit.

p.s. setting IDL IC to 100 means there's no pre-calc (interp.), in case anybody asks.
these things are feasible on fastest macs with 10.6.x.