While it was quite a while ago that we discovered that overclocking K-series CPUs might be possible on certain H87 motherboards, it wasn't until recently that two manufacturers have officially announced the possibility.
Both ASRock and ECS have officially announced overclocking features for select H87 and B85 motherboards, while ECS also added H81 motherboards to the list.
Previously, whenever users wanted to overclock their CPUs, they would need a combination of both a K-series CPU from Intel, as well as a motherboard with a Z-series chipset. Without the two in play, overclocking through adjusting the multiplier just wasn't possible. Now though, it appears that the latter of these two requirements is no longer... required. Users will still need K-series CPUs though, as non-K series CPUs have upwards-locked frequency multipliers.
Neither ASRock nor ECS has given us a complete list of H87, B85, or H81 motherboards with support for the feature, though we do know that ASRock's Fatal1ty H87 supports the "Non-Z OC," as ECS' H87H3-M4, B85H3-M4, and H81H3-A3 motherboards support the "CPU OC" feature.