I don't believe that is possible I've never tried to do it but you may be able to store LaunchBox on the network drive and use it on your PC. Is your computer a Laptop or a Desktop if it is a desktop you could get an external drive or add an internal drive (I prefer internal but both work fine). If it is a laptop you could get an external either a passport, a full size that needs external power or buy an internal drive and a drive enclosure. If your laptop has an optical drive you can get a hard drive caddy remove the optical drive and add a storage drive to the caddy. I've done this on two of my laptops then got optical drive enclosures so I can use the drive via USB if needed. There are now 256 GB SD cards that are around $70 which make good LaunchBox drives especially if you aren't storing all of your games on them that would accommodate your metadata with ease. If there is a way to store your media outside of LaunchBox I've never seen the settings for nor have I seen an request to be able to so.
EDIT Sorry just saw that this is an HTPC what form factor is it does it have room for an internal drive? Does it have an SD card slot?