If I want borderless, I just adjust my easels to form a very shallow "well" that the paper can sit into without the blades or edges having to be on top of the paper.

I use a lens aperture that assures a bit of depth of focus, and just rest the (RC) paper in the well.

The paper is flat enough to ensure that the image is sharp.

My last couple of postcard exchanges have been printed this way.

It is important to have an image that allows for a slight amount of "slop" on the edges.