Ways to displace liquids while cooking
There are many kitchen utensils which will work. My favorite will be canning jars, filled with some water so they don't float, and sealed. Food safe, can withstand the temperature, easily cleaned. One may be enough, if you find the perfect size. 

If you don't have them and want to try it with something else first, look in your kitchen for metal or ceramic vessels which can stand upright and are several centimeters taller than the sauce level after displacement. This can be a thermos flask without the cap, or even a tall mug. Just put it there, again fill with some water, and fill the sauce around it. The biggest risk is that it topples over, and you end up with a somewhat watery sauce.