sorry to bump and old thread, but we just ran into the same situation (needing to send a literal Number Pad Plus to a terminal session) and we found a solution that works without having to use a Terminal activity or remapping keys (both of which were not available to us):
“ABC[k(add)]”
using [k(add)] seems to send a literal + from the number pad, which is compatible with our terminal emulator (Mocha 5250). We can also use "ABC[k(numEnter)]" when we want to send a literal Enter from the number pad.
Hope this helps someone in the future 
Anil_G
ashokkarale
vrdabberu
Pujitha_Ande
Ajay_Mishra
Yoichi
anjani_priya
postwick
Marisa_Ontiveros1
J0ska