We study the motion of long polymers (e.g. DNA) in a gel under the inf
luence of an external force acting locally on small segments of the po
lymer. In particular, we examine the dependence of the drift velocity
on the position where the force acts and the length of the polymer. As
an application, we discuss the possibility of gel magnetophoresis - t
he size-separation of long polymers by the attachment of a magnetic be
ad at an arbitrary position along the length of the polymer. We show t
hat there is a regime where the separation of such polymers with this
'random-position beading' is possible.