The template does one name per cell so you can't overlap things on their corners.
grid-area is shorthand for grid-row/column-start/end, so you could explicitly set the column-end to be "right". That'll stretch it out over that column, but text won't wrap and I don't know if there is a way to essentially "float" that right element.
So what you could do, given you know the size of the columns and rows (or do you?) is to create a floating div inside the content that positions where the overlapping right cell is.
https://jsfiddle.net/e1hg05af/