We all know our patriarchal blessing both bestows a blessing upon us, and also ties us back to an ancestor and bestows that ancestors blessing to us. That seems to be a much more general principle.
Why is our lineage declared? So we know whose blessing applies to us, we all know the different tribes have different responsibilities and that those responsibilities are pointed to in their patriarchal blessings (which we seem to only have fragments of in Genesis 49). Even without the whole blessing, being known to us, the blessings are still bestowed, just at the Lamanites receive blessings they are completely unaware of because of promises made to their ancestors.
But what is patriarchal about patriarchal blessings. It isn't just that the person who gives them is called a patriarch. The point is, the reason we learn our lineage and whose blessing we receive is, that what is patriarchal about patriarchal blessings is that they are inherited. Presumably, given that it is called Patriarchal, inherited from our fathers.
Thus, yes, there were patriarchal blessings before the days of Abraham. As long as one had worthy fathers to inherit blessings from, there was purpose in understanding patriarchal blessings. This is something we king of intuitively recognize in the scriptures, but not in modern days.
For example, Joseph's patriarchal blessing is found in Genesis 49 along with his brothers. The blessings of Ephraim and Manassah are not recorded there. But we have no question that if we are from either of those tribes that Joseph's blessing applies to us, just as his brothers blessings each apply to themselves, but also describe the responsibility of their tribe of descendents for many generations. The fact that it is the twelve sons of Israel whose blessings are described again suggests that patriarchal blessings are inherited through Fathers.
I think Joseph Fielding McConkie used word's similar to this. You can take your ancestor's patriarchal blessings and staple them onto the end of your own. The point being that they apply to yourself. (I don't recall whether he was talking about father-line ancestors or not).