giving a lulav through matanah al menas l'hachzir

The Rosh writes that if one gives a lulav to someone as a matanah al menas l'hachzir (a sale contigent upon the object being returned), the receiver must be makneh the lulav back to its original owner in a formal act of kinyan. Matanah al menas l'hachzir means (according to the Rosh) that the original owner retains absolutely no rights to the object and therefore he must re-acquire it when its term of use expires. One cannot have a kinyan haguf l'zman - if one transfers just the right to use the lulav temporarily, writes the Rosh, this is not the same as ownership, but falls into the category of shaul, a borrowed lulav. The Rosh cites proof to his position from the gemara which teaches that a lulav should not be given to a child on the first day of Sukkos before being yotzei because the child cannot be makneh the lulav back to its original owner (see last week's posts). The Ketzos (siman 241) disagrees and writes that the mechanism of matanah al menas l'hachzir does not require that the original make a new kinyan to re-aquire his lulav. The gemara that teaches to avoid giving a lulav to a child is addressing the specific case where the owner has specified that he transfers the lulav completely to the child, but in general, matanah al menas l'hachzir is permissable with a minor. Aware that his position contradicts the Rosh and Ritva, the Ketzos cites R' Avigdor Kohein (quoted in Shu'T Rosh #35) who holds that a kinyan made for a specific duration of time (kinyan haguf l'zman) is considered a full kinyan and not called shaul, yet once the term of kinyan expires the object automatically reverts back to its original owner. I believe this is the same opinion of R' Avigdor that those learning the daf Yerushalmi saw referenced by the gilyon on daf 2 of Orlah, but maybe more on that later.