Thought you might like my (still work in progress) bottom filament extruder.
Mine had too low pressure on the filament and I also wanted to develop an extuder you can also mount on the back if you operate your ZIM with your own filament.
http://www.thingiverse.com/thing:680631
By the way: has anybody got a name or link for this 6-pin connector on the stepper motors?
printed about 50hours with the new extruder: works very well: no clogged extruder anymore! 
(the printed hands are for a 300mm high Lego figure!)
I released the final version 1.2 which works perfect - feel free to download and print! 
That link is broken.
It is: I’m at version 1.7 already so I have deleted version 1.2 - will upload it in a few hours and post a message!
Here is the latest - and (for me) best working - extruder block.
printable without ANY support (maybe you have to rotate the parts), but you’ll need several M5 to 4mm pneumatic fittings.
Forgive me, I guess I’m not sure what this does – is it just to assist feeding the filament up to the extruder?
I think that might be a 6-pin JST, connector, BTW.
The concept of the filament drive from Zeepro is flawed and with the near to no teeth on the gear does not work.
So here you have one solution to improve the grip with an adjustable filament drive.
There are two motors one in the bottom and one in the head.