Placing these books in electronic OA and offering affordable print on demand for those who need it is a solution that would deserve being examined, as it is already with the reprint on-demand of out-of-print books in the public domain by some firms such as Lulu.
This is exactly the solution adopted and used by the Australian National University ePress, for probably two years. They'd be happy to share their experiences and expertise with anyone if asked. See http://epress.anu.edu.au/titles/index.html for a description of Print-on-Demand. By keeping the issue separate - monographs really import only in the humanities and some social sciences, but there, they are the dominant currency - there is no risk of placing the archiving, green road in jeopardy. Â Books are also important for Economics, Business, Law and similar professions. Â Arthur Sale