Yes, you certainly can. While the NUC7i#DNHE NUC Kits ship with a WLAN card installed, the standalone NUC7i#DNBE board ships with this slot left empty.
Now, that said, there is something that you need to understand: This connector is keyed to support only M.2 Type E cards; it will not accept M.2 Type B nor M.2 Type M cards (i.e. it will not accept M.2 SATA/NVMe SSDs). Saying it another way, this connector cannot be used to support the inclusion of two M.2 SATA/NVMe SSDs on this board.
Hope this helps,