Set default variation hook in functions.php

Hello:

Is the a filter I can use in function.php that would allow me to set the default variation value of a product based on another value (which I have setup in a session variable)? Folks select a piece of artwork (that is NOT a product), and I have a variable set to the orientation of that artwork. The products have a variation for orientation (square, portrait, landscape), and I’d like to be able to se the default of that variation select to the art work orientation value.

Thanks so much for any help.