You ask whether there is anything in the Christian tradition that justifies going beyond the idea that the Jews would be forgiven for crucifying Jesus (“for they know not what they do”) and saying that they would actually be rewarded by God for their actions. And you cite the case of the Sufi saint and martyr Mansur al-Hallaj, who told the Muslims of Baghdad that, if they killed him, they would not only be pardoned but also rewarded, “for you will have acted out of zeal for your religion”.
I’m certainly intrigued by this possible parallel, but in point of fact, no, I know of no reference in the Christian tradition, scriptural or otherwise, to anyone being “rewarded” for the Crucifixion. Indeed, Orthodox liturgical hymnody, especially during Lent and Passion Week, is full of invective against the “Jews”. Of course, one must put this word in quotation marks, for the reproaches in question are not to be construed in an ethnic or “anti-Semitic” way. On the contrary, the “Jews” are but a “type” for all who sin against God.
There might be another way for you to work out a parallel, however. I’m thinking of Augustine’s teaching concerning the “fortunate” nature of the Fall. According to Augustine, “God judged it better to bring good out of evil than not to permit the existence of evil” (Enchiridion, VIII), an idea which reappears in the West in a traditional hymn for the Easter Vigil: O felix culpa quae talem et tantum meruit habere redemptorem, “O happy fault that merited such and so great a Redeemer.”
Perhaps you could therefore argue thus in your lecture: Inasmuch as every sin is a “fall”, and inasmuch as every fall “merits” redemption, it follows that sinners (the “Jews” being their “type) are “rewarded” for their Crucifixion of Christ. I realize this is considerably more roundabout than Hallaj! But that’s about as close as I can come.