Quick googling found an answer but it may be brand specific. This page doesn't say it but I heard from another forum that this does exactly what I suggested. Too bad I don't have ASRock mb. Atleast now I know what brand to get for my Haswell setup. I'm getting a brand whose engineers say "can be done":
XFast RAM is designed to allow users to manage the wasted memory space under Windows® 32-bit OS*, improve web surfing experiences, boost application's speed 5 times faster and reduce the frequency of accessing SSDs or HDDs to extend their lifespan.