There is a discussion in the achronim about the issur of lifnei iver. Although the gemara makes it clear that lifnei iver only applies when it is תרי עברי דנהרא - two sides of the river, meaning one is only in violation if without him the person didn't have access to the issur. However, there is a machlokes in a situation where the person had the ability to violate the issur without assistance, but he would not have violated it. The question is when one could have violated an issur without assistance, but would not have - Is provoking one to violate an issur, even when not enabling, a d'oraysa violation of lifnei iver? The Taz (y.d. 148:3) implies that so long as the person could have done it, it is not a violation of lifnei iver to provoke him to do it. However, the Chazon Ish (63:13) disagrees and holds that if you are מכריע חפצו to violate an issur that he could have without you, but would not have, is also a torah violation of lifnei iver.
A proof to the chazon ish can be brought from the gemara in kiddushin 32a where the gemara implies that there is a torah violation of lifnei iver for a father to provoke his son to him him. Although the son could have hit the father without being provoked, he would not have, and therefore the provoking is a violation of lifnei iver (one can argue that it is only d'rabonon).
One can also bring a proof to the chazon ish from our gemara. The gemara says that it would be lifnei iver to give over one's sheep to a Sheppard (if the Sheppard was suspect of grazing the animals on stolen fields). Why is this lifnei iver? By giving my sheep to the Sheppard I am not enabling him to steal from other peoples fields. The Sheppard could have stolen without my sheep. I am merely provoking him and providing him with a reason to steal. The gemara seems to hold that even though he could have done the aveira without me, since he wouldn't have it is considered lifnei iver (unless here too the gemara means that it is just a d'rabonon violation).