After hours of trying, it seems like the BK-90 was intended to be used without updates.
Waypoints updated via the ground radar just seem to be nowhere near accurate enough to land a weapon near the target, whereas a manually entered waypoint over a known target's position is always spot-on.
After a quick bit of reading up, it seems like it makes sense that the BK was an afterthought, though.
It was said to be underdeveloped, and most Swedes didn't exactly buy the excuse of "Don't worry, it's a sub-munitions dispenser not a cluster bomb!", as the Swedish weren't a huge fan of cluster-bombs as they were notorious for leaving behind unexploded ordnance that, given that Sweden is a neutral country, would, if ever being used, end up on Swedish soil.
Thanks for the help, though!