A quick way of doing this is to go into the options and put the sliders down for the CPU, do the objectives and then request a sub. Once you're subbed off, you can sim the rest of the game and the objective stays completed. However, is it to be noted that some objectives like the keep 60% possession etc can change as the game is simmed, meaning you might not get this objective if your team loses possession below the target.
Hope this helps everyone! All the best :D