There are some practical things that can be done, how practical depends on you though.
O-rings help, but they work almost exclusively towards dampening bottoming out.
You get noise from the blue switches (clears are more quiet but retain similar feel), but not just from bottoming out, you also get noise when it returns to the top of the stroke. Softer springs (blues are the softest), help on stiffer switches, but otherwise there is little you can do to stop topping out noise except dampen vibrations from it as sound is vibration.
Double thick keycaps can help some with topping out noise, but don't expect miracles. A towel, foam, mousepad, soft rubber feet under your keyboard also helps. Aluminum cases can dampen it, but it's not cheap. If you have a steel plate, switching to an aluminum one will cut down the noise. If you have no plate a plate can help, laying tracks/lines with silicone all over the plate between switches can also dampen the noise. Filling the bottom with foam of some sort will help. As mentioned, mineral oil can work, but it's messy if you ever have to transport it. Foam is less quiet, but more practical.
Bottom line, you can do lots of little things that help by dampening vibrations and altering the pitch but for the most part, a mechanical keyboard, particularly with tactile feel, and especially Blues, is going to be noisy.
