Say that a property A of x is synchronic if its being had by x depends solely on what happens at precisely one instantaneous time. Roughly speaking, A is synchronic iff x's possession of A is compatible with x existing only at one time. The definition is rough, but hopefully it will serve.
Consider the following claims:
Thesis 1: Some fundamental properties (of beings that exist only in time) are not synchronic.
Thesis 2: If presentism holds, all fundamental properties (or at least: all fundamental properties of beings that exist only in time) are synchronic.
It follows from the two theses that presentism is false.
Are the theses true? I find both of them plausible, though I am better able to argue for 1 than for 2.
The argument for 1 is by citing an example. It seems that my consciousness is a fundamental property of me. But consciousness is not synchronic. A thought experiment: diminish the length of time of an experience, say a pain. As one diminishes the length of time, the vividness of the experience goes down in proportion to the length, and is zero in the limit as the experience has zero length. But an instant of time has zero length (this is a substantive claim; those who hold a discrete theory of time can deny it). Thus, an experience that happens only at an instant would be one that we wouldn't be aware of. So consciousness is not synchronic.
It is also plausible that the brain states that correlate with consciousness are not synchronic. If one froze the brain on an instant, one wouldn't be able to tell whether it is a conscious brain or not, because if one froze the brain on an instant one wouldn't be able to tell in what directions all the particles are heading.
Plausibly, there are some fundamental axiological properties of human beings, like being well. But no such axiological properties are synchronic. (We can imagine two people frozen on time slices. In one, the particles all have random velocities and in the other they have normal velocities. The one with random velocities is in the process of exploding. So he's not well. But you can't tell that he's in the process of exploding from just the timeslice.)
Actually, I don't know if there are any fundamental synchronic properties. Maybe spatial location is, though. But all I need is the existence of some non-synchronic fundamental properties.
Now, Thesis 2 is more of an intuition based on the fact that the presentist believes in the ontological priority of the now. It seems that the presentist's reality is constituted by what is the case strictly now, i.e., the synchronic properties grounded in the present, together with what was and will be the case, i.e., the synchronic properties grounded in the past and future.
This argument encapsulates an intuition that presentism is incompatible with consciousness.