Is it possible to reduce without boiling?
It's not necessarily a practical home kitchen answer, but rotary evaporators do this, by lowering the pressure over the liquid and circulating the liquid to increase surface area.

There does exist a culinary vacuum rotary evaporator, for only $9,999.95 by special order! Note that it also captures the vapor to condense, because often the flavor you want is actually volatile aromatic compounds, which evaporate faster than the water does, so trying to evaporate/boil away water is futile.

So if what you want to concentrate is aromatic, you're probably out of luck for home purposes. If you just want something non-aromatic dissolved in the water (dumb example: reducing sugar water into syrup) then boiling/evaporation can work, though. You could certainly speed things along by using as broad a surface as possible (a large pan), gently heating, and blowing a fan over the surface. But it's still going to take an awfully long time without actually boiling.