The way i see it there are two options around this...
http://www.makergeeks.com/popofl3dprfi.html
this might not quite be ninjitzu filament but it definitly Karates a bit...
Flexible enough to bend and can be extruded... quite pricey but hey we are all rich here...
the other alternative is a thingyverse gear that confines the filament till it reaches the gears (or is it after it passes the gears).. cant remember off the top of my head..but i will look for it.
Being in Panama getting the filament is quite costly at around $40 ish per kilo shipped to miami plus another $8-12 shipping... So a pink hello kitty stamp for my princess costs me 75 bucks and 2 weeks wait cause i gotta buy the whole spool... so I will be getting these beauties next Jan...
http://www.extrusionbot.com/product/the-eb2/
http://www.extrusionbot.com/product/the-cruncher/
http://www.extrusionbot.com/product/colorants-2-oz-bag/
It Allows me to extrude my own extrusion grade prime quality abs filament (I got 100kgs of A grade extrusion ABS from my regular polymer provider as samples) and can color in one of 12 available pigments... I have 100 kgs of ABS and the way I see it I will have made back my investment on the first 15-20 spools or so... Just an idea for those of you in faraway (expensive shipping) lands.. Also it will allow me to try some cool ideas like collecting/recicling milk jugs and 3d printing in HDPE which should not be a problem assuming the melt index is low enough..
Also opens up the posibility for my wife's shop to get her own flashforge , a beanbag and trinket/jewelry/bracelet store.. www.tuspoofs.com to sell 3dprinted thingys, nametags, (wheel gears, eboard enclosures maybe) and all sorts of stuff that can be 3d printed...
ok but I ramble...
Ill look for the ninjaflex gear printing thingys...