No, and it's not easy to make it into a mask - because it takes the source and destination into account. It might be collapsable to a single mask though, I'll have to check the math.
I figured. Still, I'd find it amazingly useful. I hope there's a way to do it.
There is a way, as far as I can see.
Duplicate your layer, hit Command G followed by command E - this merges the duplicate layers transparency into a flat layer. Load the layers transparency (command clicking on its icon if you don't know). Now add a layer mask to your original layer with the selection still active. This creates a layer mask that duplicates the effects of the blend-if that you have applied. You may get better result if you now clear blending options on this layer
I have also often wondered how to turn a Blend If into a mask, so it could be modified further (blurred, for instance).
I found it was indeed possible: change the blending mode of your Blend If layer to "Difference". Then load the layer as a selection (by command-clicking on the corresponding channel icon in the Channels palette). And there's your mask, to be applied to whichever layer you want.
One potential obstacle: Photoshop does not effectively apply channels as selections if they are close to black. For example, if all your tones with "Difference" applied fall between, say, 0 and 15 RGB, Photoshop will create a completely useless empty selection. To get Photoshop to 'take' the selection, try adding extra contrast to the layer with curves. At this point you will be glad if you applied your Blend If to the Underlying Layer only, otherwise it will be thrown off and you'll have to redo it.
Hope that makes sense.