If the input DNA is less than 40 μL, can TE Solution from NadPrep EZ DNA Library Preparation Kit v2 be added to a total volume of 40 μL?

No, Nuclease-Free water shall be added to  a total volume of 40μL. The composition of TE Solution is 10 mM Tris, 0.1 mM EDTA (pH 8.0), which can be used for library storage.