Shadow is widely researched as a user interface for manipulating graphical information on large displays. The shadow of one's fingertip is used as a pointing cursor whose position and size (i.e., gain and reaching area) can be intuitively adjusted, because one thoroughly comprehend the shadow's perspective projection behavior. The goal of this research is to allow a seated user, who cannot sufficiently move his/her fingertip, to manipulate the shadow cursor. We achieve this by relaxing the perspective constraints, i.e., applying weak perspective projection model. Through an experiment, we confirmed that the pointing performance of seated users is improved in the proposed method compared with the conventional method. Specifically, the users completed pointing tasks 25.1 % faster with 54.2 % fewer errors when the target size was small, 34.5 % faster with 64.2 % fewer errors when the target size was medium, and with 58.3 % fewer errors when the target size was large.