xmodmap: Map numpad to one set of keycodes, Shift-numpad to some other set of keycodes, detected by Blender

I am able to map my numpad with, for example, an ~./Xmodmap file like this:

keycode 87 = XF86Launch1 keycode 88 = XF86Launch2 keycode 89 = XF86Launch3 keycode 83 = XF86Launch4 keycode 84 = XF86Launch5 keycode 85 = XF86Launch6 keycode 79 = XF86Launch7 keycode 80 = XF86Launch8 keycode 81 = XF86Launch9 keycode 90 = XF86LaunchA keycode 91 = XF86LaunchB

Of course, this means my numpad no longer enters numbers nor provides nav functions (Home, PgUp, etc.). Up to now, I've been living with that, but now I am using an application (Blender) that has mapped many functions to the numpad. I'm able to get by with an alteative ~/Xmodmap.numpad file with contents like this:

keycode 79 = KP_Home KP_7 KP_Home KP_7 keycode 80 = KP_Up KP_8 KP_Up KP_8 keycode 81 = KP_Prior KP_9 KP_Prior KP_9 keycode 82 = KP_Subtract XF86Prev_VMode KP_Subtract XF86Prev_VMode keycode 83 = KP_Left KP_4 KP_Left KP_4 keycode 84 = KP_Begin KP_5 KP_Begin KP_5 keycode 85 = KP_Right KP_6 KP_Right KP_6 keycode 86 = KP_Add XF86Next_VMode KP_Add XF86Next_VMode keycode 87 = KP_End KP_1 KP_End KP_1 keycode 88 = KP_Down KP_2 KP_Down KP_2 keycode 89 = KP_Next KP_3 KP_Next KP_3 keycode 90 = KP_Insert KP_0 KP_Insert KP_0 keycode 91 = KP_Delete KP_Decimal KP_Delete KP_Decimal

but switching between them is a hassle. Can I just use xmodmap to have my numpad act like the first file normally, but act like the second file when I hold Shift?

When I use xev to inspect the keycodes, Shift-numpad doesn't give different keycodes than normal numpad, it just sends a keycode for the Shift key separately from the numpad key.