Unfortunately you cannot do that. If you want even 1 RA2 Full product (hybrid keypads) you need to use ALL RA2 Full stuff. Unless you want to buy a separate hub for 1 device but that would be a waste. Don't get me wrong I use them and I love them, but know what your getting they are not cheep.
Also know that the writing on the buttons will be small. You more or less need to know what they are, as they are hard to read (unless you have 10/10 vision)
The keypad below is zoomed in pretty close and still not easy to read.
Also check out this post on In-wall button controllers for other idea options if you do not want to go with RA2.
