you have some pcb traces hacks to implement a full 4 wires setup
and the crocodile grabbers who get some modifications too
the only thing i haven't found is a calibration procedure for them 
or i totally missed it ? sure you have the open and close mode
There are no trace hacks required, if you study the schematics and of the chip set utilized (where ever they are), you'll see that the chip set invokes a full Kelvin 4 signal measurement with Low Current, Low Sense, High Sense and High Current just like the Lab LCR meters.
http://www.cyrustek.com.tw/wp-content/uploads/ES51920.pdfNote the reference to "
4-wire terminal with guarding measurement" in the data sheet.
The TL-21 Alligator Clips route the Current and Sense wires in a 2 wire shield cable for High and Low. The Current and Sense are terminated together (soldered) on one side of the Alligator clips towards the end, the shield is not connected.
So if you remove these High and Low cables you have H-C, H-S, L-S, L-C separate TL-21 PCB trace holes available. There are the 3 separate blades in the TL-21 that engage the DE-5000 body, the blades are double sided and two blades are used for High and Low Current and Sense lines (4 lines total), the other Blade is double sided Guard.
We used 4 coaxial cables and soldered each shield to the Guard Ground on the PCB TL-21 which is the internal meter analog ground.
Here's a couple images showing the standard DL-21 with Alligator clips and the modded DL-21 with the 4 coaxial lines and BNC connectors, note the 4 separate active lines in each.
Anyway, hope this helps understand how the DE-5000 is configured.
Best and Happy Holidays,
Edit: Haven't found any way to calibrate, nor files related to such. Actually we haven't even tried to look at any of the firmware/software, will have to leave this to the more qualified folks.