It is possible but will violate UL standards. UL requires the input cable to be short because, the Input is not protected by all the safety features and shutoff like the cable beyond the charging station. A short input cable is less likely to be damaged.
Ok thanks Chris. Duly noted. I'm curious though, what happened to the fourth lead coming out of the 14-50 plug? The assembly instructions only show the two hots and a single ground, which presumably is shared with neutral?
Neutral is not used at all so there is no need for the wire. On our NEMA 14 - XX we remove the pin all together so the plug will fit NEMA 14-60, 14-50 and 14-30.
For Level 2 charging on a NEMA 14 OpenEVSE uses 2 hots and ground.