Penelope Maddy addresses both the issue of spatio-temporal location and causal relation of universals to us in the context of (non-Platonic) mathematical realism see Perception and Mathematical Intuition and Mathematical Epistemology: What is the Question. First, causal theory does not require direct causation, some knowledge is by inference, including inductive inference from simple cases, which may well apply to universals. So causal relation can be mediated by an inferential link to direct interaction, and elementary universals, like finite sets and numbers, are present, she claims, in the content of perception of sets of physical objects. In other words, she rejects the "sense data" theories which reduce perception to sensation of particulars (this is supported by cognitive science studies, see Metaphysically, what comes before the cognitive ability to make distinctions?). Here is her response on causal efficacy and spatio-temporal location of universals:
Consider the following case: P needs two eggs for a certain recipe, reaches into the refrigeratorf or the egg carton, opens it, and sees three eggs there.... the various numerical beliefs acquired on this occasion are perceptual, and I further claim that they are beliefs about a set, that is, I claim P acquires the perceptual beliefs that there is a set of eggs before P, that it is three-membered, and that it has various two-membered subsets...
I must agree that many sets, the empty set or the set of real numbers,f ore xample, cannot be said to have location, but I disagree in the case of sets of physical objects. It seems perfectly reasonable to suppose that such sets have location in time-for example, that the singleton containing a given object comes into and goes out of existence with that object. In the same way, a set
of physical objects has spatial location insofar as its elements do. The set of eggs, then, is located in the egg carton - that is, exactly where the physical aggregate made up of the eggs is located.
It is interesting that Maddy's only credited source of inspiration is Gödel, who suggested that abstractions in our experience appear due to "another kind of relationship between ourselves and reality... [other than] the action of certain things upon our sense organs". But it is well known (from Gödel himself) where he got this idea. It was Husserl's categorical intuition/ideation, see In what fundamental ways, if any, does Husserl break with Kant? And indeed Maddy's theory of ideal perception is largely a redux of Husserl's, but with explicit realistic commitments.