What model in the Clinet Card? If it is at DWA-542, you might be able to find a D-Link ANT24-0230. It's three foot cable lead may get you out of the way of one of the "line-of-sight" limiters (desk enclosure?).
That antenna may also imporve connections to other D-Link clients -DWA-552 (pci) and DWA-556(pci-x).
Otherwise he may need to get a higher end AP (DIR-655) or Client (DWA-552, DWA-556, DWA-140, DWA-664)
Then there is "cable it up"......