I usually plant giant sunflowers on the veg plot to accompany the runner beans and French beans, and to add a colour splash. The added bonus is that the dead flower heads attract sparrows and other small birds to feast on the seeds. Win-Win. Composting them is another matter. If you do this, you'll need to cut the stems up quite small so they rot at the same rate as the rest of your compost - and you will need a sturdy cutter and strong hands!
On an exposed veg plot you may need to stake your giant sunflowers. If you tie them to your runner bean poles and the wind catches them, you will be in danger of losing the lot!