It has been done for the 9XX series... the #45 # 78 carts
That it can be done on the HP 9670 printer is doubtfull the sponges are for
the color so small ~7ml .... you will need to develop your own based on
existing systems ie for canon and epson bear in mind they use removable Ink
Tanks a big plus ...
HP chose not to go that way except in a few pro models.
Bob Headrick could elaborate on that
Refilling works fine on the #56 and #57 up 10x refills