Yes. Instead of giving the parent li a ‘position:relative’, give the parent ul a ‘position:relative’. That would align the child ul (I’m assuming you’re using absolute positions for the sub-levels’) with the parent ul, instead of the parent li. An absolute position element is positioned relative to an element that has a relative position in which it is placed.
Edit: Wrong answer sorry, since I realize that you’re talking about the third level submenu.
I’m not sure if there’s a better way to do this, but you could use a div as the drop down element(thus absolutely positioned). Then the ul placed inside the div could have a relative position. The third level position would then be absolutely positioned in relation to this ul.