You can't selectively interpolate some texels and not others.
However, this doesn't have to be a problem. If you make all of your transparent pixels black, and then use the "pre-multiplied alpha" blend mode (i.e. src=1, dst=1-srcAlpha), there won't be any artefacts around the edges.
Interesting, I have the same problem. Please help me understand how it works (I am using pre multiple alpha already).
It is the sampling from the texture that will get a bad color, isn't it? So a position between a white non transparent pixel and a black transparent pixel would become gray 50% transparent? If so, using pre multiplied alpha won't help as long as the colors are wrong?
There is another possibility: Using mipmaps, but you have to create the mipmaps yourself. That way, you can use an averaging algorithm that ignores transparent pixels.