You might try a macro type program, like
AutoHotkey, to remap keys. AutoHotkey is an extremely powerful and versatile tool, however in order to accomplish something like this the process is very simple.
Once AutoHotkey is installed it requires a script to run in order to perform its functions. The scripts are just text files with an .ahk extension. In order to do a basic key remapping you would create a script containing something like the following lines:
j::NumpadSub
k::NumpadAdd
Once running this will effectively make your J and K keys (or whatever key you specify as the initial key to rebind) function as the numpad subtract and add keys.
A list of keys and functions recognizable to AHK can be found
here.
Also, we don't know what type of notebook you have but many models can simulate extra keystrokes that they don't physically have by use of a special key, normally this may be called a function key (not to be confused with F1-F12), labeled as "Fn" and perhaps a special color like blue or orange which may also match other keys on the keyboard. Just as an example, I have a notebook next to me which I would press the combination of Fn+P to produce the nonexistent numpad subtract key.
