Have a 'custom polearm' like the 'Custom Sword' option.
If item like the 'wooden staff' was made shorter and had a attachment point at the end,
you could have a varity of blades to exchange and attach,
without having to buy another foam staff or complete polearm.
This also would allow different length's of foam pole's by having extra pole length that could be attached, and easer shipping because of the ability to break down the length.
(I would suggest a socket and a pin like a katana and have the tang be very long)
To sum it up,
a blunt normal staff end could be attached at each end to allow a short staff, or replace them with another leangth of staff, a blade, a blunt end(like a foam rock or something), normal staff end.
This allows post purchase user chosn lengths.