Layne Norton did this in some studies... In between meals the BCAAs spike protein synthesis but also let it fall fast enough to allow for another spike when you at your next meal. The research also showed that keeping sustained high blood amino acid levels actually blunts the protein synthetic response. What is needed for the protein synthetic response is a rise in blood amino acid levels.
It should also be noted that for for BCAAs to elicit a protein synthetic response their needs to be a complete spectrum of amino acids present. So if you take them on an empty stomach you won't derive as much benefit as you would if you had a small serving of protein beforehand or ate a meal a couple of hours prior.