Seems like a bit of a silly idea to me. Not sure how you'd define "co-pilot duties". One of the reasons we have multi-crew a/c is redundancy - if one pilot becomes completely incapacitated, the other is qualified enough (at least on paper) to handle things. The idea of having a disparity between the training (NOT experience) received by each crew member seems like a bad idea to me.
Just my 2p.
V1R