Just in case anyone is interested, this is one of the things that HotkeyNet can help with.

It allows you to define each number pad key separately for each left or right modifier or any combination of them, and for NumLock up or down.

That's a lot of combinations. Leaving out the ones that are impossible to press with two hands (like LCtrl RAlt NumpadPlus) but only including combinations like this:

LShift NumpadEnter
LAlt LCtrl NumpadEnter
LAlt LCtrl Clear

HotkeyNet allows you to define 380 different hotkeys on the number pad.

But that's if we limit ourselves to the regular modifiers. HotkeyNet also allows people to define custom modifiers, which allows combinations like this:

R NumPad7

If we include custom modifiers, it's possible to define tens of thousands of hotkeys on the number pad.