How do I place a long wire to make the EMI and inductance minimum?
I would imagine skin effect will disrupt your calculations quite a bit: -



The above picture tells me that at 50 kHz (sinewave of course), the skin depth of a copper wire will be 0.3mm - as you are using 2mm thick wire for your experiment, most of the current will be travelling around the outer perimeter of the wire and your cable resistance will be significantly greater and that's just at 50kHz. If the signal you hope to measure is a square/pulse wave (with harmonics at 100k, 150k, 200k, 250k, 300k etc, the resistance for these higher frequencies will be increased. At 150kHz, the skin depth will be about 0.1 mm.


  How should I place this wire?


I wouldn't bother because it probably won't meet your expectations. Picture taken from here.