If you have access to a set of I/S fender struts and the trunk mounts, look into swapping the stock rails for those. Then get yourself a piece of aluminum plate and size it to fit between the trunk mount rails.
(I'd have to mock one of these up to see if the plate is best positioned overtop the edges of the mounts, or if it should be positioned underneath and a filler panel used to bring the surface level with the mount edges.)
After your plate is in place, lay out the positions for the SW-Motech mounts (shown on Phil's Concours 14 Rack site)
http://www.philsfarkels.com/and drill the required holes then install the parts.
I have Phil's racks on both of my Connies and run a Givi V46L with them. It's a very solid arrangement, even at high speed. You should be able to duplicate the concept on your Valkyrie fairly easily.