This is for OFP, but should work fine for ArmA.
In your init.sqs execute an script to move the camera away from initial player position. You may also want an initial black screen, but not really needed, it would be better to have the camera pointing to some nice location. This way you will never see the player's initial position. Place as many markers as needed for insertion locations (visible markers with a short description), force map and anim it for first insertion point. Now show a dialog (defined in your description.ext) with a single list box with the long description of the available insertion points, each time current selection changes, map anim again to the new marker. Your dialog should have also an ok button, once pressed you hide the map (forcemap false again), close the dialog, move your group to the selected insertion point and delete the camera.