After the project is finished I apply it to the backer by turning it face down, put some Alene's Tacky Glue in a plastic lid (like a butter tub) and 'paint' the glue on the back of the project and then place it on backer. Then I take a piece of 3/4" plywood and place it over the top, weight it down with a gallon can of paint and let dry for about 2 hours.
I have never had any project separate using this method even with the back coated with the BLO mix or any other finish.
~~~GB~~~