I believe it has been done on a Vietnamese-plated bike, even though I haven´t done it personally (and don´t know how legally, etc).
But I´ve crossed the Poipet-Aranyaprathet border, and I would choose some other place to try that! It seemed like a real ___hole on the Cambodian side, and also the Thai authorities got us stuck there for hours, even though our (Thai-plated) bike´s papers were fine.
The border near Koh Kong might be better, but from Siem Reap, that´s a long detour. There should also be one border crossing (Ban Pakard / Phsa Prum) located some 10-15 kms west from Pailin, and that one seemed pretty quiet & relaxed, though I´ve only crossed it coming from Thailand, and this was already some 5 years ago. I think that´s the one I´d go for!