As these are non-dairy, what are you using as the liquid instead of milk/cream?
Many traditional techniques used to extend shelf life – such as using an invert sugar like trimoline, glucose syrup, or honey – are not going to be available to use as they may not be vegan (honey) or are highly processed (trimoline). Your best control methods are to minimize free water (known as water activity - do you know the aW of your centers?) and reduce the amount of oxygen incorporated into the centers as oxygen is required for stuff to grow.
I would also recommend storing everything cold – down to 34F if your recipe is not designed to be frozen.