We explore the possibility of controlling the orientation of adsorbates, and their adsorption site, through alignment of a beam of gas-phase molecules prior to the surface reaction. To that end, we carry out classical trajectory simulations using ab initio data for the specific example of the I-2/Si(100) adsorption reaction. I-2 is found to adsorb with the molecular axis roughly parallel to the surface plane independently of the initial alignment. The orientation of the molecule in the surface plane and the adsorption site are controllable through alignment of the gas-phase projectiles. Our results are explained in terms of the surface properties and the reaction dynamics, and the extent to which and way in which they may be generalized is discussed.