This is not something that's currently possible. It is somewhat related to improved preloading and to automatic default selection -- all of these feature requests have to do with collecting more than one survey's worth of information for the same entity.
Do you actually need access to the day 1 information when collecting data on day 2 or simply a way to link the two records? In fact, do you really need separate forms for the two surveys or could you possibly have a single form that has instructions for the enumerator to save the current work and return the next day to finish the encounter?