If you can plan ahead for fixturing, add enough stock allowance to drill a couple of dowel holes in the first machining position. Suppose you were to add some extra length or width to permit this.
Then machine a subplate (or another board) with two dowels to mate with the fixturing holes in the part. Set up this subplate and locate the reference point over one of the dowels. Usually, you might place the two dowels on a line parallel to one machine axis, to facilitate setup of the fixture.
Then, flip the part over in cadcam and relocate your X0Y0 over the one dowel. Post new code from that location.
A final step will be some sort of procedure to cut away the excess material containing the dowel locators. You might do this with a saw, on a project like yours. Or, you might reclamp the part where it sits and write a couple of short programs to cut the excess material off the ends of the part.
First you get good, then you get fast. Then grouchiness sets in.
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)