procedural generation - How can I generate biome borders?

I'm looking for ways to generate random biome borders (like what Minecraft has).

One technique involves choosing specific biomes based on (eg) a rainfall map and a temperature map. But that just determines which biome to place, not where the borders between biomes are.

I don't want to use quantized Perlin noise directly; that would generate certain quantized values strictly within other zones, whereas I'd like finer control over which biomes can abut others. For example, in Minecraft one can see mountainous terrain, forests, plains, or deserts right next to the ocean.

Many of the solutions to "the biome problem" propose computing the whole universe in a heuristic manner. I want to generate infinite terrain, and to me that suggests the algorithm be strictly functional: given an X,Y value (and a world seed) the algorithm can easily spit out a biome value.

So, my question: what are some techniques for identifying random, non-trivial-sized, contiguous chunks of terrain to be of a given biome?